2003 Chevy Tahoe Serpentine belt tensioner pulley won't sto

03 tahoe, 118000 miles, 5.3L V8 (T VIN), automatic

One of the pulleys started making a loud squeal like the bearings were going out. Narrowed down to tensioner pulley on serpentine belt. Replaced pulley with new bearing but noise hasn't gone away. With the engine running and the squealing ringing loud and clear I can shoot some lube into the front of the pulley and the squealing stops but then slowly comes back. I've tried installing without washer, re-installing old pulley and even installing new pulley then backing the bolt off a little bit to give it some 'room'. At times it quiets down or goes away after engine heats up and other times it just squeals no matter what (freeway speeds, slow speeds, cold engine, warm engine) so i'm really clueless. Any help will be much appreciated! Thanks!