ok so i was looking around for a beater/work truck and found a guy i work with wanting to sell one. its an 89 isuzu with a 2.6 I-4, 4x4, 5 speed.
This is the info I got from the guy

The engine has been replaced and has around 20,000 on it, the truck has 170,--- on it. Its in pretty decent shape, a couple small rust spots, the cowl is rusted but not thru yet and the pain it oxidized on the roof and hood. He told me that it ran but needed engine work, someone else told him it was valves but not sure as hes no mechanic. I went and checked it out, we put a battery in it and fired it right up to my surprise. There was no smoke or anything but it seemed that the engine rocked back and forth a little more than it should, especially when revving it or something (maybee broken mount) and it also seemed to have a light rattle but not bad, the p.o.s. cavalier I drive to work rattles far worse. The only thing is I was told it seems like it has no compression, it wont pull itself up even a small incline.

The story I was told was that he was driving and it started knocking and kind of shaking that he could feel thru the whole truck, like in the shifter and everything. He thought it was knocking like it was low on oil so he drove it home and parked it.

any suggestions? Ive gotten some advice allready that it could be just the clutch gone in it since it seems to run good but wont pull itself. any way to tell if its engine trouble without tearing into it?