If you can find one to borrow or rent use a cylinder leak down gauge, I use them when I do a 100 inspection on aircraft engines, it will let you know if you have a valve or piston ring problem, I do all the cylinders and write it down , I do this on the aircraft I work on and enter the info log books for past history of the engine , if all are good next thing I would look at is plug wires , a bad plug, or something in the ignition system, if that does not show up any thing last I would check for a worn cam , lobe almost gone, these are a few ways we can point you in the right direction on fixing whats wrong . As Wittsend said give us some numbers , and a extra note is to keep the fan belt in great shape , if you lose it it will run hot quickly, and Will crack a head in no time, the later 2.8s in the bronco II/Rangers had all three belts go over the top water pump pulley to help with that problem , (ask me how I know) good luck ,