I have an Jaguar xjs (1991) AND ITS TAKING TOO LONG TO CHANGE GEAR FROM 2 TO 3, CAUSING THE RATATION TO GO UP AND WASTING GAS. And possible you to know that power to be happening. Thank you very much.

 

When was to last time you had it serviced? Fluid and filter? Possibly the vacuum modulator, thats what controls shift points. Check vacuum lines to modulator for leaks or plugs.
Try Googling turbo 400 troubleshooting, vacuum modulator