My boss has a Trooper, he likes it in general but he's lately been having an issue with clogging oil passages. Apparently some of their engines are prone to forming deposits that restrict oil flow to the valvetrain. The only remedy is to open up the engine and manually clean out the deposits. You can delay that by using a thinner synthetic which can get through the constricted passages better than a thick conventional oil. A sign of the problem is valve train clatter at startup when the car is cold. Once it gets sufficient oil to the valves
I'm not sure if '91 or the I4 is affected so you'll want to look around and see if its ok. Also, if this is going to be vehicle used only occasionally (just as a camping vehicle, to drag stuff home from Home Depot, etc) it can last quite a while with low oil flow to the valvetrain on startup. I wouldn't want it as a daily driver though if it already was having issues.