Just read a post on here from 2006. A guy had the same issue you are having with an 02 silverado. No one provided any insight to fix the problem, just stated a bad brake design by GM. They were also stating that their inner pads wore much quicker than the outers. 02 silverado uses the same pads as the avalanche. Maybe try a different brand/auto store to see if you can get a better fit.
I agree with bad Bowie2. Hopefully they just gave you the wrong ones. I also looked up the front pad part number for an 03 avalanche and it is the same as a 02, 4x4 and 2wd. This leads me to believe you don't have a "half year" truck that needs a different pad.
Did you compress the caliper piston(s) back into the caliper? If not use a c-clamp and push the piston back in. If you have 2 pistons on your calipers make sure you press them both in at the same time. Use the old pad as a bridge across both pistons and put the c-clamp in the middle. When you are all done with your brake job you will have to "pump" the brake pedal to get the pistons back out to where they should be.