hey spencer try putting about 200 lbs of something or other in the back end against the doors and then see if it does the vib, thing it sounds like it may be driveline angle and with the increase torque at that boost you could be twisting the pinion up to high , when you feel the vib start take the throttle back a bit and see if it stops , those things are notorious for the pinion angle vib, mine is driving me nuts , i am going to have a double cardan drive shaft made for it , the the angle wont matter much JERRY