First thing to check would be the trans fluid level. The trans dipstick is right next to the oil dipstick. Check it with the engine at operating temp, and the car idling in neutral. DON'T FORGET TO SET THE PARKING BRAKE!!!!!
Next would be to see what color the fluid is. Use a white paper towel to wipe the dipstick. Should be red to pinkish. If the fluid is brown, it's burnt and needs to be replaced.
I would guess that it's going to be one or the other of the above. Your other option would be to flush and replace the system. Our trans take a specific type of fluid and it could have the wrong one. DO NOT buy a trans flushing product. They are a waste of money. ATF is a great solvent / cleaner on its own. You will need to drain the system, fill back up, drive about 20miles then repeat. This is because you can't drain the torque converter in the car, and it holds around 4qts. Three times would be optimal, but twice will suffice.
If that doesn't help, post back here with the results and we'll try and help some more.
Happy Jeepin' & Keep it rubber side down...