Hi and welcome, I'll give you a bit more info which seems to have got confused over on the other side. I can't post on there as I got myself a lifetime ban for advertising this forum (and being critical of the attitude of the mods over there). If you get gearbox fault as soon as you turn the ignition on or start the car, but before selecting a gear, that is a voltage problem. Going into limp mode and either cutting out (especially when hot) or failing to start is quite likely a CPS problem. A gearbox going into limp mode and doing odd things, is likely to be a genuine gearbox fault. Have a read here http://www.ashcroft-transmissions.co.uk/frequently-asked-questions/4hp22/4e-faq-s.html which describes your problems almost exactly. Ashcrofts will do you a recon gearbox or you can take a punt on a secondhand one. The gearbox on a 4.6 is the 4HP24 rather than the 4HP22 fitted to the 4.0 litre and diesel models. The 24 is also longer so you need a gearbox from another 4.6, preferably a later one the same as yours (not sure if there are any differences between gearboxes on the GEMS and Thor but better swap like for like in case there is). If you swap just the gearbox and retain your original transfer box, make sure you change the gearbox output shaft oil seal or you'll be taking the transfer box off again to change it (or dumping ATF all over the floor).