pinion angle help please

[88Stanger]

Ok, so i have a 1969 C10 that is lowered 4" in rear with springs and 2" blocks, the front is dropped 2.5 with springs and drop spindles. At say around 40 to 45 miles an hour there is a vibration, harmonics. The drive line is new single piece that replaced a 2 piece that did produced the same vibrations, so this tells me it is Pinion angle. Here are the angles:
4L60E tranny is from front of truck to rear = 7 degrees down
Drive line is at 1 degree down (from front of tranny looking to rearend)
Rearend is 5 degree up (from rear of truck looking towards the front)
all measurements are done with truck on 4 separate blocks, so suspension is fully loaded. I have trailing arms not leaf springs
Where i get lost here is what to do. Should i install wedges to rotate the rearend to decrease the "positive" pinion angle? If i am not mistaken, if i move the 5 degree pinion angle to "Down" to 3 degrees of up angle, then the Driveline angle would increase to -3 degrees. This would then take the rearend pinion angle to a net "0" pinion angle, is this correct? If that is correct, that would then make the transmission angle increase correct? damn i am confused here and i know it is something simple i am just missing.
Thanks for any and all help here.