2001 Aztek ABS & Traction Control Problems

My 2001 Pontiac Aztek GT FWD (V6) has had problems since purchase with the wheel sensors. The original problem (occaisional brake vibrations) was never resolved under warranty because the dealer kept insisting they couldn't feel it. It finally became so bad another dealer checked the ABS computer for errors and found a bad wheel sensor. Sensor changed, orginal problem gone after 4 years!

Unfortunately, the story continues. The car now has 136,000 miles on it. I have had to replace the wheel sensors in the front (and the bearing assembly as they are one unit costing over $300) three more times since. The situation lately is a complete failure of the antilocks and traction system (all warning lights on and ABS applied at every stop!). The last one on the front left wheel lasted 1 week before the ABS and traction system started having problems again.

Is anyone else experiencing continual wheel sensor problems like this? Are the parts I am getting bad from GM? Or could there be some other problem in my car that is causing them to fail so continually. What else can the mechanic check assuming it's not a bad sensor issue?

Thanks.
-Gary.