I put the clutch in and it stopped slipping, but most of the problems I was having are still there. I get a real bad vibration at higher speeds. I start noticing it at about 50mph and then the faster I go the more vibration I get. When I let off the throttle the vibration completely stops until I throttle up again. The worst vibration by far is at high rpms in 3rd gear though, which I don't understand at all. When I shift from 2nd to 3rd the truck starts vibrating more and more until about 2800rpms, then the vibration just completely goes away??
Also there is a rattling when the truck is idling in neutral.
There is also a lot more backlash than there should be when accelerating and letting off the throttle.
All of these problems were there before I put my new clutch in, but have gotten MUCH worse since the new clutch. Also, when I pulled my old clutch and flywheel, the throw-out bearing sounded like a bucket of bolts and my pilot bushing came out in several pieces.
What do you guys think is going on? Do I just need to get my tranny rebuilt or do you think its something else?
Give me about another year and I'm going to have a completely rebuilt truck
Chris
But still held up to full throttle from a dead stop. 
Try prying the shafts back and forth, checking for end play. Wouldn't hurt to jack up the truck and rock the wheels and drive shaft, check for play in the diff first. Check the oil in the diff too. Like Jon said, check the u-joints, they can cause vibration too.
