Mickey_D wrote:
I had a 2005 Sierra CC 5.3 and it pulled remarkably well. You did have to let it rev and just lock out the OD but we pulled way too much (12K plus pound plus utility trailer with brakes) and it never overheated or felt totally underpowered. The one thing that it was not was fast, so limiting towing to 55-60 was a good idea. I would not worry about swapping gears unless it just does not want to start moving, just lock it out of OD and don't worry about running it around 3000 rpm.
Before changing the rear end.
lock out OD as mentioned above & find out what your max torque is at what RPM & stay there when pulling grades.