My Jag does fine in "D", but when I put it in manual mode, it immediately gives a transmission fault and shows restricted performance. Any ideas on this problem?

 

Cable adjustment issue, if it's not an R then it doesn't have a dual linear switch that also needs to be adjusted. Proper adjustment of the trans cable can be tricky buisness. There are two big jamb nuts that hold the cable to the J-gate. I do them by feel, it took a long time to get the hang of it. If the cable is adjusted correctly and there is still an issue deeper investigation would be required.