Wheel hub and bearing needed replacement. mileage is 76,000.
Is this unusual? on 2006 Buick Rainier

Other good features indicate to me that such a problem is unique and GM should stand behind this wear. How do I contact GM?

Asked by for the 2006 Buick Rainier
These are common on Raineir, remember, GM went broke. They had some horrible quality control issues with some poor quality vendors, it wasn't just the Unions. There are many, many people after GM for these bearings, so it may be a wait, but I wish you the best.