Its a 85 swb c10 with Mcgaugheys 4.5/6 drop..Motors fairly new,trans is new, u joints are new and ahafts balanced..Installed 4 deg shims to correct pinion angle and it still vibrates! I shimmed trans up just a little thinking driveline needed a little more angle,vibrates worse..So,what now?? It vibrates 45 -60 then gets better..any suggestiins?