As the other posters noted, you need to minimize all angles on the driveshaft. And normally all the driveshafts would point "down", and in keeping with that the pinion on the rearend would always point "up". I suspect it is the angle from the pinion to the rearmost driveshaft that is giving you the trouble. I'll bet if you put an angle finder on the pinion yoke you will find it is pointing "up" by a few degrees like it should be. You're a racer so you should have an angle finder in your toolbox anyway, and if not they are cheap at Harbor Freight and the like. The solution will probably be to raise each carrier bearing slightly until you have the same angle at each joint. Or you could look at it with the angle finder stuck to the top of each section of driveshaft and calculate the difference between each. For example (and I'm picking these numbers out of the air as an example) the first driveshaft might be at 88 degrees (2 degrees from level) and the next shaft 86 degrees and the last 84 degrees which would also be 2 degrees from the actual pinion angle. The idea is to have the same angle at each joint. Also of note, when I was talking to my driveshaft shop about lengthening my truck he told me the longest shaft they would build would be 54". Not sure if that was due to strength or vibration issues.
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