Differential or brakes?

I'm not sure what your Jeeps problem is, this is one of those problems where you have to see the Jeep, tho i'm no pro, and dont know everything I would think it's not your trans.

If it were your trans it would "slip". If the engine is "raceing" or reving high as your driveing it might just be the trans....

I do hope that you find the problem, and if I can be of any help in the future just let me know..