While having the P38 on axle stands yesterday so I could grease her nipples I noticed some slack between the rear prop and the transmission is this normal?

There's always a bit of slack anyway, but if you can turn the prop back and forth and hear a clack, clack from inside the transfer case as you turn it, that is the chain. It can be like that for years but as soon as it starts to jump a tooth when you pull away sharply or on a hill, then the time has come to change it. I did mine just under a year ago after it had done around 410k but it had reached the stage where I had to be gentle on the throttle when pulling away from a standstill.

Thankyou will keep an eye on it for now. Many thanks