driveline angle experts??

[johnymac]

Hello all,
I am in need of some advice here.

I have a 67 c10 stepside. I dropped it down 6” in the rear using 6" lowered springs, and 3” in the front, 2” dropped spindles, 1” dropped springs.

A couple of years ago I swapped out the TB350 for a 700R4, had a new driveshaft made, one piece shortened 3” from the shaft for the TB350, new ujoints.
The truck had an annoying high speed vibration that I wanted to resolve.

So recently, I took my initial measurements and purchased 6” coil spring shims for the rear.

I have the transmission shaft and the pinion where I believe they should be and work. The truck seems fine until I put into overdrive then it feels like the driveshaft is going to come thru the floor and I actually lose power in the truck. I have checked the timing to make sure it’s not the timing, timing is correct. I should also add it seems to run fine vibration free until put into overdrive.
I am planning on changing plugs and wires next, but prior wanted to ask for any feedback. The truck did not run like this prior to these new changes.

I can not move the transmission up without cutting the floor of the truck, which I really rather not do.

Current measurements are:
Transmission shaft 5 degrees up
Pinion is 5 degrees down.

Transmission slip yoke bearing cup is 5 degrees up
Pinion yoke bearing cap is 5 degrees down

Driveshaft bearing cup:
2 degrees up in the front
2 degrees down in the rear.

Driveshaft angle is 1 degree up

I believed this to be an Operating angle of 3 degrees
The transmission and pinion are at the same angle, but are opposite.

I can have the shaft and joints checked, but the weights are still on the driveshaft and there is no play when I grab the DS and try to move.

Am I missing something here, are our trucks different? Any advice or suggestions sure be appreciated.

Thank you.