Alright, as the title says I've got a strange vibration when under a load (aka normal driving... aka 3/4 throttle or more lol) but ONLY when reaching the 4000 rpm mark and then it continues until the shift into 3rd and disappears. This started happening as soon as I dropped the truck basically and obviously it is bothering the heck out of me.. I am kind of stumped as to what could be causing it, because (correct me if I'm wrong) a u-joint, off-balance driveshaft, or anything of that sort should be consistent throughout the entire gear span shouldn't it? Just curious if anyone has had this same issue or not before? I couldn't find anything already in the forum.