Turns out it was the O-rings on the cylinder sleeves. Dan and my dad and myself pulled the head and pistons and a couple sleeves so far. Gaskets were fine (although still need to be replaced) and the pistons and sleeves looked like new. We're thinking that it was previously overhauled because they look so good. Apparently when they put the pistons in they sheared or otherwise damaged the top of the three O-rings on each cylinder. The middle ring on one was busted completely, and the other one is solid. It seems that the engine must have been overheating frequently to turn the rubber into plastic. Bearings look fine. Injector cups are fine. Injector nozzles are very dirty, so we'll have them cleaned and tested tomorrow. Maybe that's where our loss of power is from.
So it looks like (fingers crossed that the other four cylinders are good) we'll just have to buy a top gasket set and O-rings!
My build thread:http://www.skoolie.net/forums/f11/build-thread-for-haulin-oats-and-goats-11237.html#post113500
A gal, a guy, three cats, two dogs, one rabbit, and one goat, traveling the country together.