Driveline vibration?

Ok I'll run down the list. The drive shaft is in phase with each other. The u-joints were all replaced by me 2 days ago. The vibration is related to speed and does it in 3rd or 4th. Original engine and came with a 318. Engine is smooth when reved up. Clutch action is smooth, no chattering. I marked the two shafts with white paint to put it back together the way it was, what I may try is to rotate the rear shaft 180 degrees and see if that helps. Since the joints I took out were not original, someone might have put it together 180 out,