as you know I have an a518 [46rh] OD trans, lots of potential drive line angle issues, so I had a Alum shaft made here in houston by a well known company, $750, FOUGHT & FOUGHT a drive line vibration, ie EVERYTHING possible LOL, pinion angle,trans angle ect, I gave up, blew up my 8 3/4 & had to get them to shorten the drive shaft $150, now the vibration was WORSE, took it back to them three times for a rebalance ,,, NO change, in desperation I ordered a Strange steel custom shaft $450 & it changed the vibration considerably but at high speeds it came back, I called Strange & asked them what RPM they spin the shaft for balancing, they said, 500 rpm was the fastest they spin them, so I did the old chalk marker test on the shaft on jack stands at 60 mph, the chalk marks were at the same spot as the welded on weights, so I cut them off & ended up adding weight almost opposite of where they had them, the vibration was ALMOST gone but at 120mph it was still pretty bad, so, I called Mark Williams & asked them what RPM they can spin the shaft, They said as fast as you want, so I had them build me a new shaft $650 with their better yoke, the car is SMOOTH as GLASS !!!!!! another one of my expensive lessons learned the hard way & yes I have the large u joint 1350