sounds to me like its over fueling the system. bad main injector will cause this or possibly a bad injector housing. if it seems to run when you relief pressure off the system this seems to be the more likely scenario imo.

also if no coolant was going through the intake circuit i would bleed out the cooling system (while the engine is running) to get all the air pockets out of the system.

cat did a recall on quite a few of those a while back requiring the dealership to go out and replace many of the injector housings. (these were all early tier II engines though if i remember correctly)