I've got a 99 XJR with 127K on it. I've only had it a few days but I've noticed two odd things about the transmission:

1. When on the highway, it rarely wants to kickdown, even when I've floored it and am pushing away at the little switch under the pedal.

2. At 50-60 MPH, shifting from D to 4 doesn't seem to do anything at all. Shouldn't this take it out of 5th at this speed?

The transmission works fine otherwise. I also looked briefly at the small "I floored it" switch (I'm sure Jaguar has some other name for it!) and noticed it appears to be adjustable. Should I dare adjust it?

 

You can undo a connector for that switch, it's hidden under the carpet, and put a meter on it to see if it works.
Mine didn't and after disassembly and cleaning it was fine. Beware, there are small springs and ***** that will fly out !

 

You can adjust the cable at the throttle body, take off the intake elbow, then you can see the throttle blade. A few posts saying what a big difference it made.

 

If you have the throtlle wide open, what rpm does it shift at in sport mode? Mine was 4500 until I cleaned the switch, now it is 6,000.