I finally received the answer to this problem with my '06 Rainier CXL. The front gear pack (in mine) needs to be replaced. Vehicle is driving AWD, all the time. Expensive repair- $1600. Mine has 93+K miles, the engine is in awesome condition. To repair or not to repair... that is my struggle.
You wasted your time at Advanced Auto --because they won't explain what needs to be done & you wouldn't understandanywayGo to a repair shop--they have to use the proper professionalscan tools & testing procedures, along with reference materialIt has to be component testedThis procedure has been with us for 32 years now,any time you get any dash lights or codes