Tensioner pulley. Mine whined for the better part of a year, could never figure it out. Truck would shift rough, made a God-awful racket when driving. Two weeks ago it threw a belt. Thought it was just crappy, replaced it, and it threw that one, too. I tried the pulley and realized it was frozen. Luckily I have a 3.5 Trooper engine in the garage, so I pulled the pulley off of and put it on the VX. Runs like a champ, no more whining, and the engine shifts a *lot* smoother.

The VX pulley, when I pulled it off, had shredded metal and jacked bearings inside. People say to start w/the AC pulley, but I'd start with the cheapest (and easiest) part to replace first. As my truck also had a tendency to overheat in hot weather w/the AC running full blast, I'm thinking the pulley might've been the problem, as well. I'll know next summer