I have a 99 Suburban that has a shake at approx 70 mph to 80 mph. I first bought a set of new tires and had the front end aligned. The shake was still there. I had the drive shaft checked at the local driveshaft shop and they said the new tires may have flat spots. I have replaced all of the shocks, had the front end completely rebuilt and had the front end realigned. The shake was still there. I had the vehicle load tested and they said it may be the tires so i bought another set of Hankooks to replace the Mesa tires. I have also put dial indicators on all four wheels and there is no runout. I have replaced all of the brakes and still the vibration is there. The transmission shifts fine and the engine has had the upgraded vortec injection system put on it so the engine runs smooth as silk. I have heard drive shaft balancing can cause the shake but ive had it checked and they said they could replace it but couldnt find anything wrong. Any ideas?

 

Is it 4wd, if so check the front shafts U joints. Even though you may be in 2wd the shaft still turns.