really bad squealing at higher rpms

Every time I get up some rpms, in any gear, I get a serious squealing going on. I have had new belts put in, no change, I tried taking the belt off of the alternator completely to rule it out, same issue, so it is not the alternator. The A/C was disconnected years ago, so it is ruled out. I was told maybe the fan clutch? How else can I diagnose this? The squealing at high rpms has me shifting very early to avoid it, so I wind up in 4th gear already before 40 mph, and I cant get it up over 55 or the squealing is really bad. The engine seems to be running very well otherwise. (V8 7.5 460) I do not knowe the exact rpm as i do not have a tach. Please any suggestions, or ideas of how to diagnose this? Thanks