OK, I think I'm inside my own head here. I'm chasing a vibration on my 1994 C1500 short bed truck. I suspect it's just the empty bed hop at this point but I decided to upgrade to a 5 inch aluminum shaft (thanks Tahoe donor) and have a look at the drive line angles. Looking from the drivers side and following the slope front to rear the Trans angle is 6.7, drive line is 2.7 and the pinion is 6.4 , all sloping down or toward the back of the truck. This gives me a working angle of 4 degrees on the front joint and 4.3 on the rear joint. I can't find a definitive answer on acceptable operating angle or is the difference of .3 is enough to be an issue. It seems the rear pinion angle can be expressed two different ways and mean the same thing, this was my method: What's the consensus?