my 94 XJS 6 cyl'dr has started shifting very hard going up and down in gears. This doesn't happen all the time, but occasionally the transmission light will come on and the hard shifting starts. If I stop the car, turn ignition off and then start up again, every thing is fine, till the next time it decides to act up. I asked on the "my mechanic" web site and was advised it would be the transmission computer. Put a salvaged computer in, but still the same hard shift that feels like a kick in the back.
Ideas anyone?
thanks bobbo

 

I have the same configuration in my XJS. And, had the same experience. For me the fix was a simple R&R of the trans filter and four quarts of Amsoil trans fluid. The light went and stayed away and the shifts softened up. Of course, what worked for me may or may not work for you(see disclaimer).

 

from Bobbo; Tried the flush and filter last fall, a few weeks before storing the car for the winter. Thought this cleared it up, but it started again a few days later and is still an intermittent problem this spring. Maybee I should flush and filter again.