Tires: Shaking/bouncing, steering wheel, drivetrain

Question
My 1999 3/4 ton GMC 4wd Suburban developed a very bad shaking and vibration front and rear.  It is extremely bad between 65-70 mph.  I knew the wheels were bent and the tires scalloped, so I replaced all wheels with new ones, and new tires.  Yet, I still have the bad vibration between 65-70mph.  Where do I look next?  Vehicle has 76,000 miles and oem shocks were replaced at 40k.

Answer
Butch,

wheel end vibrations are usually confined to either the front - in the steering wheel - or the rear - in the seat back.

If you have both, it's logical to assume it is in the drivetrain - although that's not 100% reliable.  Worn U joints are common vibrational cause, but I suspect you need to have someone look at the whole vehicle.  There are a lot of places that a vibration can originate from.