I know this is an old thread, but I just noticed it here. I have a 2002 Suburban. At about 85,000 miles it developed a "shake" in the front. It felt like the front right. It felt like one wheel was on the rumble (wake up) strip on the right side.
I had the 'burb to 2 Chevy shops and 3 independent front end shops. 4 sets of tires, 3 alignments, 2 inner tie rods, 2 new sets of rotors, a right hub and a set of front shocks later it is still going on. All 5 shops find nothing else wrong.
I now have 170,000 miles. The above repairs gave some releif to the shimmy, but nothing ever took it away.