I would contact your local Chevy Dealer.......they can check your VIN # for any open campaigns......
I noticed there are two for your vehicle:
#14772 2005-2006
#12221A 2008
Chances are the torque sensor has already been replaced, but couldn't hurt to check....
Sorry, just read the campaigns.....they had a 10 year limit from the day the vehicle was originally bought.....
Found another one #10183A, but again 10 year limit....
One thing you need is a scan tool that reads, "C", or Chassis codes....your average scan tool or code reader does not read these.....a scan tool that reads ABS codes/data, can read these.....
Possibilities are: intermediate shaft, steering gear binding, steering shaft bent, sensor, wiring, power steering assist motor, etc.