Tourque converter, or transmission issue.

[Lowfill]

While returning from OurY in our 2000 xj with auto transmission, 242 transfer case, and 456 gears. We developed a bucking sensation while driving on flat ground while in overdrive. Downshifting to 3rd did not seem to help the problem on flat ground but did help when climbing hills, Vail, and Eisenhower. I was thinking the tourney converter might be slipping but not sure. Checked oil when I got home and seems fine smells a little warm but still red. Any help would be appreciated.
Phil

[Jim]

Likely not your issue but I'll toss this out as you mention bucking sensation:

In my 68 Ford Ranch Wagon the driver side rear wheel bearing failed - outboard end of the axle. This caused the axle/drum brake assembly to occasionally "catch" the brake shoes which caused a bucking sensation, noticed on smooth road.

Do you have a tach on the dash / did you notice (or feel or hear) any engine RPM change when it happened?

0.02

[Hypoid]

Without a test drive, and On Board Diagnostics, and other electrical testing, I would bet 50-cents on a Throttle Position Sensor.

[Lowfill]

I do have an RPM gauge, and there was no change in rpm when it happened. It only lasts for a second or two but it is like the tranny disengages, then reengages, causing the jerking sensation.There is no stalling or speed limitations while this is going on.

[Hypoid]

Next time you are cruising on the highway, keep your speed steady, and with your left foot tap the brake pedal. The RPMs should go up a few hundred and drop back to normal as the torque converter unlocks and re-locks.

[Jim]

Engine light on? Any codes to display?

[dieseldoc]

Not the TC
These things are very reliable
You might have an issue with wiring causing the lock issues.

I am along the lines of something more like the TPS as well