96 Jimmy trans
 

I have a 96 jimmy sls 4×4, trans is starting to slip. Will a 99 Jimmy trans be direct swap or anything else? Of course both have the 4L60E, but not sure if there's a difference between these years.

Fluid and filter been changed?

Yes it has been. My issue was that i would run 70mph at 2200rpms, then it would jump up to 3000rpms and wouldn't shift. I had to replace the rubber grommet the dipstick is in at the trans, and the lower trans cooler line at the radiator was loose and leaking. Tightened out up and so fast so good, but haven't really had a chance to test it out yet and see if that resolved my issue or not.

Are you sure it's not the TCC disengaging. 2200 sounds right for it being engaged in 4th. Try shifting to third when you think your problem is happening. If it then downshifts, what you are complaining about now is the TCC not staying locked. Are you trying to run faster than 70 or go up a hill and keep the TCC engaged? The ability to do that may depend on how well your engine is running as it unlocks TCC at some point when you have increased engine load.

Thats just normal expressway driving. I drive like an old man, so i don't run it hard at all. Always take my time, besides its 24yrs old and the motor is solid and runs great. Since I've tightened the fitting and rplaced the rubber grommet, i haven't chanceti test it out. The odd thing i can't figure is it would only do it when I'd get home from on friday, and let it sit for a few hours, then drive it 45min to go coyote huntng is when it'll do it. Go hunting for a couple of hours and it doesnt do it on the way home.