I took the Hummer to have it safetied and got it back with a vibration when reversing or driving foward @ around 1000 rpm but goes away when speed increases.
The mechanic I took it to would seem not to like Hummers seeing all he talked about was if I had 2 jobs to pay for gas
I don't want to go ask him If by chance he forgot to put something back and the wheels fall off.

 

Are the wheel lug nuts tight? Take it back...

 

Yes they are tighten. I took all four tires off my self to scrub the back side of the rims and tires.
under the hummer there are 2 long rods one the left and one on the right side which starts from somewere around the drivers seat and runs towards the engine, each rod is held up by 1 bolts. the bolt on the drivers side looks like its longer than the other side. I'm tempted to tighten it but I dont want to throw any suspention calabrations off.

 

Look at the driveshaft to see if there are any marks on it. It's possible they could have bent it with a floor jack or lift.

 

good point, I'll take a look... I also tried tightening some 18mm bolts under the hummer last night with no results.

 

I've had this vibration for over a year. It's only when I hit 40mph that I feel the vibration in the gas pedal. I had dealer check everything, front end, pitman arm, checked for placement of cables in engine to make sure they aren't leaning against something. Once I pass 40mph it goes away. I have no idea what it is but it is very annoying. I would love to find out what is causing this one day.

 

How about a bad tire?

 

You should find a shop in your area with a Hunter Roadforce Wheel balancer those are really good and they should find the problem.

 

It's not the tires in my case. When in reverse mainly, or in drive, foot on the brake pedal and the engine revs within 700 TO 1000 RPM. The vibration is in the dash and foot pedal and it is very annoying. The hummer Idles @ around 500 to 600 RPM with no vibration.

 

My last guess is drive shaft - good luck!