My truck is a long bed 4X4, 4.3 litre 5 speed manual, purchased used. The truck has a vibration eminating from somewhere in the engine, clutch, or front end area. The tires were pretty worn when I bought it, so I thought they were the problem. Bought new tires, and no change. The vibration starts about 45 mph, regardless of gear. Vibration lessens as speed increases. The steering wheel shakes, the 4x4 shifter vibrates so bad I had to bungy cord it to the seat to calm it down. Depressing the clutch while @ 45 mph ceases vibration, so I thought it was in the drivetrain. Tried turning the driveshaft 180 deg. No change. Could be the clutch, except I've also noticed the vibration is not consistant from day to day. Seems like it's worse on colder days, but not always the case. Knowing that the 90 deg V-6 is naturally unbalanced, and that GM added balance shafts to compensate, maybe the engine is causing it. I'm also considering the possibility that the computer is over-leaning the fuel mixture, which could cause the engine to run rough. My truck's warranty is over, so I've been trying to come up with fix myself, but it looks like I'm going to have to break down and take it into a dealer for an analysis. Will update after I have it looked at.

I've read lots of complaints about similar vibrations, but have yet to see where anyone reports an adequate solution. It is also helpful in these forums if owners give as many details about their vehicle as possilble. When some just says "2000 GMC truck", and leaves out type of engine, trans, drivetrain etc., it's makes it hard to compare problems.