The 4.0L is NOT a low compression engine. It has 8.5:1 compression, I believe, which is pretty much the same as every car that can run 87 octane.
I believe a previous owner abused this truck a bit, because the original engine died around 110k miles. My mechanic was shocked. One of the pistons had cracked- a freak occurance, he said. It happened half-way to Ocala (I'm in Bradenton), and it ran the rest of the way to Ocala, and back, on only 5 cylinders. The 4.0Ls last a long time because they are a neutrally balanced engine- they don't vibrate like a V-shaped engine would. Also, they have more bearings on the crankshaft than a V-shaped engine. The 4.0L has 7 main bearings where most V-8s only have 5!
My other pickup (which now belongs to someone in Ocala) has the 4.2L in it. That has somewhere around 300,000+ miles and, while it has the bare minimum oil pressure, it still runs strong. The previous owner figured that he would just run it as long as it held out and then rebuild it when it finally died. Over a decade later it was still running when he sold it to me. I decided to put money away for a new engine when that one died... and years later I sold it with the engine still running just fine- it wouldn't die! It's not like we took it easy on the engine, either... it is a 4x4 Jeep truck, after all!
Anyhow- regarding Cherokees, get a '93-99, as those are the best years for them. The Cherokee (XJ) is one of the best vehicles ever built, an extremely versatile design. Not terrific gas mileage though....