Phantom vibration, not the obvious, please HELP
 

So ive got this 04 4wd blazer and to make a long story short it has this vibration that starts at 50 mph and ends around 70. It cruises beautifully at 80 mph. I can feel it in the seat and pedal only when my foot is on the gas. If i remove my foot it stops and when it gets really bad i can feel it in the steering wheel. Now to keep this simple im going to list all the parts recently replaced. If anyone has any new suggestions please share them.

tires have been rotated, balanced and are fairly new.
Parts Replaced:
•Most all of the braking system, pads, rotors, calipers.
•Rear axles, bearings & seals (both sides)
•U-joints on the rear driveshaft
•U-joint as well as cv-joint on the front driveshaft (from T-case)
•Both front CV-axles
•Upper & lower ball joints (both sides)
•Wheel bearings front [including hub & speed sensor (both sides)]
•struts/shocks front & rear
•Tie rod ends complete

Good luck & thank you in advance!

was the vibration there before all these parts were replaced or did it show up after some of them ?

yes it was there before all of the part changes im starting to think maybe a tranny or tcase mount. I dont beleive the driveshafts are bent at all they seem to be just fine.

Jack the rear off the ground, use all your jack stands to make it stable, chock both front and back of the front tires, and run it up to the speed it vibrates the loudest. What the noise does under those conditions will tell you where it is or isn't.

I see what you are saying you replaced, however given the fact that you are feeling it in the steering wheel, that kind of says it is in the front. I would first guess an imbalance in one of the front wheels. Try rotating again, and see if this affects anything. I know from experience if one of the tires is difficult to balance, it will likely be mounted to the rear of the vehicle. Then, when you go to rotate, you suddenly have an issue you didn't notice when it was in the back. Another less likely condition could be a warped rotor and a binding caliper. If the caliper begins to bind with heat, it will stay somewhat clamped onto the rotor, and if that rotor is warped it will feel like an imbalance. You would likely have a noticeable pulsation on braking. You would also likely have a pull when letting go of the steering wheel.

I would rotate the wheels, and test drive before doing any further diag. If the vibration goes away, bring it back to whomever balanced your tires, and have them re-done.