Vibration on accel

I am looking for a little help here, I have an 89 XJ, I have replaced the entire suspension with teh heavy duty CROWN suspension from 4WD. IT rode good, alitle stiff, but I expected that, after a while of driving it, I installed a 2" Rusty budget boost into the jeep. This was the front spacer, and rear shackles and new stab shock on teh steering. I re aligned the front end and all my numbers are good, one thing I noticed was at about 30-40 I have a vibration in the drive line, above that it goes away. I looked at the angles on the driveshaft and it "looks" ok. I realize that this is sort of a no brainer, but I was looking for input. I was thinking of dropping the t-case down about 1/2" to try and compensate the angle issue. Sound good, or is there a better idea. With 235/75 R 15s my rear is setting at 33" from top of fender to ground, and 32.5" in front. Thrust angle is near perfect at 0.04".

i had the same issue with my 96 i dropped the t case and put 1 inch spacers, that eliminated the vibe..... you can buy them or just make em your self i used SS tube and cut them to size