if it's just at high speed are you sure it actually IS your driveline? an unbalanced or flatspotted tire can do that to your axle which is obviously attatched to your driveline. blown shocks will make that bad too and mine are blown as s*** haha check your tread and also it might be your engine/tranny mounts. mine vibrates even at idle and I don't really care I paid $400 for the whole pile from a meth-head so whatever haha check it over. if everything works then... it's cool? check your bearings. how much play is coming out of the transfer case? there's a million places for vibration to come from and make other things look like they're busted.
