2006 GMC Sierra high speed vibration

[Furious5150]

2006 GMC Sierra 1500 crew cab 4x4. Bought it with a 3 inch body lift. 2 years ago I put on a 3 inch suspension lift (blocks in the rear and torsion keys in front). Tires were getting worn out and truck had a hop to it, so brand new tires (33's) 4,000 miles ago.

Since putting on new tires I have replaced:
-both front rotors (they were warped)
-front brake pads
-pitman arm
-idler arm

Still have the hop. Cant feel it in the steering wheel and very little in the seat. Mostly in the floor boards. Hop starts at 50 mph and stops at 70 mph.

Front end is stiff since putting on new torsion keys in front.

Have had new tires rotated once and balanced twice with no change.

I know my rear shocks are shot and my front shocks are almost done.

Before I throw anymore money at it, I just wanted to get some opinions.

[Furious5150]

One more thing. The truck doesnt make any clanking, humming or any unsual noises. Tie rods and ball joints seemed ok too, no play in steering since replaced pitman and idler arms. And its not a scary hop, just very annoying.

My thoughts are bad Ujoints, unbalanced drive shaft, or just bad shocks????

[Furious5150]

Update-

New shocks, raised tire pressure to 50psi, and backed down torsion keys 4 turns and no change!!

[Furious5150]

Helllooo?????

[gmtech1]

With the suspension mods done to the truck, it could be any number of things. May have something to due with the increased driveline angle. Worn suspension bushings are a possibility also. Without feeling the vibration, it's a little difficult to pinpoint.

[MikeCStig]

This may sound a little out of left field, but it's a thought. This is assuming you have the stock automatic transmission.
You have some big ass wheels on your truck, which has an effect like increasing gear ratios across the board. If your transmission computer hasn't been calibrated after these changes your shift points will be the same, including shifting into overdrive at around 50mph at less than half throttle. In my experience the overdrive gears on GM transmissions are pretty high with regular wheels, but with 33 inch tires? The vibration may be from the engine dropping to very low RPMs and fighting it's way back up to a more normal range while the torque converter is locked and you're in overdrive because it doesn't know any better. When you get to 70 mph is very likely the point where you're back in regular operating range and therefore, no more shakes and vibrations.
If you can turn the overdrive off, or if there's a tow/haul mode that often disables the overdrive, try that and see what happens.
If that kills off or even reduces the vibrations, my strange theory just might be right, and if it is, look into engine and transmission computer mods.