Mostly in third gear, but can also feel it in 2nd at higher rpms and 4th before you accelerate a lot. Only really shakes when accelerating or engine braking without the clutch engaged. When I put the clutch in, it doesn't vibrate. Nor in neutral. I just replaced my U-joints in my rear driveshaft thinking that was the problem, and it helped me in 1st and 2nd but it still vibrates pretty bad in 3rd. When I took out my rear DS, and put in in 4wd, it ran fine with no vibrations. This rules out the clutch problem for me. Any ideas? Is it my DS? Rear diff? Did I somehow mess up my U-joints? Any help or encouragement would be appreciated.