HELP: Hopping/ knocking under acceleration
I have a problem. It started yesterday and now its getting worse. I accelerated on the highway doing around 60mph. All of a sudden I had some sort of hopping feeling from the rear end. Not sure exactly how to explain it. It kind of felt like the tires were bouncing or something. It had the feeling of being pushed a little really quickly, or something smacking under the truck or something. And it continued until i let off the gas. Now its doing it at lesser speed and more often. Almost every time the truck is under any sort of load such as accelerating on any type of hill. This is under a normal amount of acceleration, just getting up to speed.
I'm not exactly sure how to explain it, but I tried to explain it to my friend the other day. He told me to check my U-joints for any play or movement. There was no play when I checked it on the truck. Should I take it off? I'm not sure what to look for after that anyway. Any help would be great, I want to fix this before it breaks something else.
2001 4x4 offroad, 4.0L, Body lift, 285 BFG A/T