Again go to the truck specific forums, the ford gold is the main suspect for clogged egr/oil coolers. Get catapiller ELC but dont use the ford gold. The ELC is a pink/purplish in color, nothing green and I dont think the orange color is any good either.
The forums will also recommend a coolant filter just like the big trucks have (and school buses) I also run a amsoil bypass oil filter setup on mine. Do you have access to a scan gauge of any sort? again try to find someone familiar with this setup and have them take a look. Not all gm or dodge products are purfect either so you can also find a dog in them. Just read thru their forums for their issues. Buying anything used is buying a pig in a poke, be it ford, gm or dodge. No matter what you buy, be sure to have some extra funds available to fix whatever you find. old dodges have block and dowel pin issues, gms had wiring issues and fuel pumps. So there is no gauranties that any of them will be problem free, but ya need to go to the right forums and research the engine of choice you are interested in.