89 4.0 renix AW4, It shifts really quickly and won't downshift. Tried adjusting kickdown cable but no help. Also did flush and filter change. If I put it in first it will hold first till redline then shift. If i put it in drive it will quick shift through all gears in less than 100 feet. shifts at like 1500-2000 RPM's

 

Does your XJ have the "power/comfort switch"? The reason I ask is my XJ does the same thing yours does if I keep the switch in the Comfort position. If I keep it in the Power postion all the time it shifts perfectly. My tranny actually feels like it slips between gears if in the Comfort position. So, I have literally driven it in the Power position for the last 2 years and it runs fine and still gets 18 mpg on the highway.

 

Transmission control module is mounted on the lower panel on the passenger side of the dash. Could be bad as it controls the tranny

 

Yes it has power/comfort but it doesnt't seem to make a difference in either position. I unplugged the TCU and it shifted manually, I was told that means its working?

 

If you unplug the TCU and the tranny shifts fine manuallly that means the tranny is fine and that you have a TCU issue.

 

Alright i changed the TCU and now it shifts through the gears better than before but wont go into 4th. I get to 50mph and it feels like the trans is slipping but it just wont shift to OD????????????