I can see both graphs now, haven't had a good look at the one I couldn't see before yet. But the thought occurs - If the reader is getting the units so far wrong maybe it's getting something else wrong too, we can't be certain that it is even reading the correct fields / data set from the ECU. I would try a different reader on it before going much further because if it's not showing correct data it could be completely misleading, if a different code reader showed data closer to what we might expect it might point to the problem straight away.

I had considered that the tool may be scaled incorrectly. I assume that the scaling is a function of the tool not the ECU. Which may or may not be the case. I am going to do some direct comparisons this weekend on both Rovers. Maybe i can spot something. If not i will re-evaluate how to continue. Maybe I need to purchase another diag tool or possibly a scope.
Any information on suggested diag tools would be helpful. I keep seeing this SSD tool mentioned but cant find any information on it. I would like to know what that one is.
As for a scope, the Pico Scope is one that i have eyeballed but not sure which model i would need.

Well just to throw another level of insanity into this puzzle.
Updated my GAP tool and then started logging some numbers from both Rovers. I did not see anything unusual for a bit but then a second code popped up, P0507. Which comes up as Rpm high idle air control. After looking at the manual it mentions air leak between the MAF and throttle body. Yea ok, i didnt tighten the plastic intake runner. So i tightened that up, Cleared the adaptive values again and cleared the codes. Now it is miraculously fixed itself. Readings from both banks match and no MIL. Made at least three separate start attempts to see if the problem returned. I then removed the intake and reinstalled it loosely to see it the MIL comes back. Three starts later and so far it has not returned. While im not ready to call it fixed yet, i wont be able to do much with it until spring when i can actually drive it.
I have a hard time believing this is a result from a loose intake tube.
However I wonder if it is possible that this could come from the previous owner using standard 87 octane fuel. Which is not recommended on the SC models. I put 5 gal of 93 octane into the truck this morning before doing anything This is the first time i have put fuel in this truck in almost 2 years. And knew about the fault when i purchased the truck.
Latest readings.
https://drive.google.com/file/d/16R7iTCNvlFe9FOJ8zxcBly-yhMDk6dj-/view?usp=drive_link

Modern fuel with 10% Ethanol degrades quite rapidly, in 2 or 3 months, so if you've been running it on 2 year old fuel, it will be very stale so wouldn't help with running. With the modern cats and emissions stuff on a modern engine, you probably wouldn't notice it, but normally you can smell stale fuel in the exhaust, it stinks.

Yes im familiar with stale fuel, I run my boat as close to empty as i dare every fall for that reason. Refresh the fuel in spring by at least doubling what is in the tank. Much more noticeable on carb engines. Fuel injected engines are no where near as affected by this. Usually only suffer some power loss. There was probably only a gal or less of fuel in this thing when i dumped the 5 gal in but the fault was there when i bought the truck and it would have had fresh fuel at that point.
Its bizarre to think that stale or low octane fuel could/would cause a correlation fault, without throwing another fault. But that is the only thing i did, unless my gap tool was not properly clearing the adaptive values in previous attempts.

Because I run my P38 Range Rover on LPG (Propane), I keep some petrol in the tank to use much like the spare wheel, to get me home if I run out. Sometimes that can be in there for months at a time and the exhaust really does smell disgusting when running on it. I winterised my boat a couple of months ago, usual advice is to fill the tank and put fuel stabiliser in it. With a 150 litre tank, that isn't going to happen but I've got an electric pump so pump the tank dry and put the fuel in the cars.

Last year I filled my boat fuel tank for winter storage and added fuel stabiliser, it was fine when I used it in the spring but the fuel was only stored in the tank 5 months. This year I bought an electric pump, disconnected the hose from the fuel filter / water separator, connected the electric pump to the fuel hose and used that to empty the boat tank into jerry cans, from jerry cans I filled my car tank and the missus' car tank, dumped the first half gallon because it was discoloured and smelled off. Start of this coming season I'll put a jerry can of fresh fuel in the boat tank and pump it back out (into jerry can and into a car again) just to rinse the boat tank before filling and reconnecting the fuel hose to the engine filter / water separator.

My car runs on LPG / propane too, I convert vehicles to run on propane for a living. The system on my car injects propane in vapour form and the vapour needs to be under more pressure than on Gilbert's system, the higher pressure means vapour is more likely to condense back to liquid unless its heated so my system's pressure reducer / vaporiser needs to be a little warm before it can vaporise propane, which means the engine has to start and run for a short time on petrol in cold weather until engine heat has warmed the vaporiser up a little. I think my car took longer to start on the old petrol I pumped out of the boat. I used to fill the boat tank with E5 fuel thinking it'd store longer/better than E10 in case I didn't use the boat for a while and for winterising but when I started using the boat more I switched to E10. I decided to empty the boat tank this year because I knew most of the half tank lof E10 still left in it had been in there a few months by the end of the season, topping it up to full with fresh fuel and adding stabilisr might've left it OK to use by the start of this coming season but if it 'went off' I'd have wasted a full tank of fuel.

Heh old fuel in your supercharged Rangerover... Well that was a curveball! But we should've asked, just wouldn't expect anyone to do all that testing and change components without checking how it ran with fresh fuel if the fuel in the tank was a couple of years old lol. The ECU on supercharged Rangerovers is quick to point to faults if any of many aspects seem off. For example on most engines if you disable the evap purge system by disconnecting the purge valve electrical connection they'll give a fault code for the open circuit connection but nothing else or if you disable the evap purge system by clamping the purge pipe from the valve to the engine there'll be no fault detected at all. But on supercharged Rangerovers if you disable the evap purge system by clamping the pipe the system is sensitive enough to detect it isn't getting any flow on the evap purge pipe, it messes up fuel trims and make it point to a MAF problem. I think maybe you were getting cam position related errors because it wasn't getting as much bang from cylinders firing as it expected due to the old fuel. I'm pleased it sees sorted now.

Yea i would have thought that that would lead to a different code. But it seems that whoever designed this system does not use the same logic we use.
In the pervious post i mentioned the idle air control fault. There is no idle air control on the truck nor mentioned in the manual. The manual only says the fault is from an air leak between the maf and throttle body. By my logic if its not on the truck it cant fault out so this should have shown an engine lean code not IAC code
The fault was there when i bought the truck almost 2 years ago. And the previous owner was driving it until about a month before i bought it. He sold it because of the correlation fault. I bought it an just stored it for the summer with repair plans for last winter but they didnt materialize. There was not much fuel in it to begin with and no reason for me to put more in. But since the fault already existed there was no reason the think that might be an issue. But it makes me think that the previous owner was to cheap to pay for premium fuel.

Don't forget that some codes are manufacturer specific and may not be the same as the generic codes.

Yea they are doing their best to put everyone out of business except themselves. And make vehicles a non repairable.

Or so you have to buy the dedicated code reader rather than a cheap Chinese generic one. They are heading down the non-repairable route anyway without specific test gear. A mate runs his own garage and needs to use his Snap-On £3k a year diagnostics just to change brake pads on a lot of modern cars with electronic parking brakes as you can't just push the pistons back in, they have to be told to wind back in by the diagnostics. Just the sort of thing to stop the owner being able to carry out his own maintenance.