Hey everybody I'm new to the forums but have a big problem. I have 1975 mustang that I've been working on for a few years and am trying to work out all the bugs. Recently I put a tremec tr-3550 in the car and with that I got a bad high speed vibration. It starts at around 70-80 mph and gets worse with speed. I know its somthing in the drivetrain because no matter what my rpm is its there. I've tried 3 different drive shafts and none solved the problem. So I thought maybe the diff so I put a different one in and it's still there. I've heard about driveline angle and am not really sure how to check it or what the acceptable difference is. I've also changed the tranny with a standard t-5 and it didn't solve the problem. I am going crazy trying to figure this out so any input would be much appreciated thanks.