om617a help

[pjl]

Sorry to keep bugging you guys, but I have some more questions, and who better....
I have the engine running reliably in my unimog, although, not perfectly.
It creates good power at higher rpm. It has what appears to be one cylinder that isn't firing properly. At about 1500 rpm there is a noteable thudding(not quite nailing sound) which I think turns into a buzz at 4000+ rpm(this might be flywheel balance). This weekend I will start by adjusting the valves and throwing some diesel injector cleaner in. I already adjusted the IP with home methods from here. Any way to determine if it's set right. It will run all day at 4000+ rpm on the flats without overheating 180'f max, on the hills it's a different story. Low speed high rpm 2000+ cfm electric fan can't keep up, has hit 230'f at which it dumped it's coolant. The diesel is basically hard mounted in the mog with no way of changing that reasonably. I need some suggestions for sound deadining material. This thing is loud and has a pretty good resonating low freq vibration at low rpm and buzz at high rpm. I'm running a K&N filter, I'll try the stock oil bath on it to see if what I'm hearing is intake noise.
I'd appreciate any constructive input.
PJL