Lmao. I wanted to put a pun in the title... Anyways, my ass end likes to bounce up and down. Tires are balanced, and there's no noises coming from the axle or wheels, so the bearings are good. I'm thinking it'd be the tires being so poorly worn. Anybody wanna second this? If not, what else could it be? It seems to just be the passenger side, not as much the driver's side. I'm really thinking it'd be the tires, because it had a bounce since I bought it. Another thing.... It only really does it between 35-40 mph and at highway speeds it's noticeable. And when I say noticeable, I mean the entire freakin truck shakes up and down. Soooo, ****ty tires? Errrrr.....?