Just bought my 2004 jaguar xj8 4.2l with 183,000 miles on her, I recently developed a problem where it will shift fine until I accelerate hard, then let out of it and it doesn’t want to go back into 5th or 6th gear it just hangs out @ 3000 rpms when driving 60 mph, but if turn cruise control on it drops right down, I’m lost hopefully someone can help! Thanks

Is it in Sport mode?

It does it with sport mode on or off. If I take off nice and easy and keep the Rpms below about 3,000, it will shift all the way through but if I accelerate a bit harder it just stays in what I believe is 4th gear and maybe sometimes it might go into 5th. I tried earlier today to slide my shifter over to 5th and then back to drive and it seemed to drop the Rpms a bit, but every time I set the cruise it will always drop into high gear and cruise.

In Sport you'd almost expect that. In non-Sport, not so much.

The reason cruise works is (I understand) some combination of having special maps for cruise and in any case cruise implies let the car do what its programming says is best (probably most efficient MPG).

I think your car may be one where the adaptive learning isn't quite doing what you want - or else some minor fault such a s sensor slightly off that's fooling things a little.

You could try having the adaptations cleared and see if it then behaves as you expect but TBH I'd just use cruise more

You also could try looking at as many sensors (via OBD) as you can in case one is a little wrong but not enough to flag codes.

Thanks for the info! I will get my hands on a scanner and monitor it and see what I can see!

In case you want to try clearing the adaptations you'll need a specialist tool such as IDS/SDD.