I'm stumped on this one - went for some very light offroading last weekend to go paintballing, and now my truck's developed a fairly harsh vibration. It only occurs when I'm moving, from around 20 to 40 mph. And only when I give it gas - it totally disappears when I just coast along. The first thing I checked was if any of the weights on my wheels or driveshafts had falled off, all seem to be intact. U-joints all seem fine too. Come to think of it, the vibration only seems to happen in 2nd gear...though that might just be a coincidence. I haven't really had time to check through everything due to work. Any ideas what it might be?