9 XJ trans Problems

I just purchased a 93 XJ that will not shift into second or third gear until you reach 3500-3750 RPM. Once in third if you let off the gas the tach will drop down to about 1500. If you give it gas after it drops it seems to rev freely until you hit 3500 and then grabs again. Also once you reach 75-80 mph it feels like it shifts to overdrive and cruises at 2000 rpm unless your speed decreases or your going up a hill. This transmission is out of a 96 XJ.
Is there a computer issue or some kind of sensor that would cause this?
The trans was changed by the previous owner and gave up on it when the swap did not fix the problem.

any help would be greatly appreciated

I would check by making sure it has the coorect level and type of fluid. The type is mercon dexron not atf+, if it has atf+ types it will shift weirdly. The second thing is the tps sensor has somewhat an effect on the tranny shift, i would check that too.

pete