I've read some post about people having bad experiences with some of the GM online parts houses and I'd like to put in my two cents.
First, I don't own a GM Truck - I own a 2001 Olds Alero. That said - I found GMPartsGiant.com from doing a google search. I was looking for 2 rear speakers my wife blew out (after 10 years). These are "bi-amp" speakers and you can't find them at the after market Auto Stereo stores here in Las Vegas, NV - and the dealerships out here charge unbelievably high prices for just about any part.
So I input the Alero VIN number and chose the part I was looking for. It came back with a different part number than was on the original speaker and their terms and conditions state all sale are final unless the part is received damages. So I called them to make sure this new part number would work - they were curteous and helpfull. They said it would - and they were right. Both speakers fit perfectly and hooked right up with the existing wire harnes quick disconect. The new speakers even came with the mounting bracket, which surprised me.
Price was good - even with shipping ($9) they were less than having the Auto Audio shop install after maket speakers that would not have worked. (Price + shipping was $117 for both speakers).
As for delivery - I placed my online order Tuesday afternoon and received the speakers via UPS on Friday afternoon. I wasn't expecting them until the following Tuesday.
I'm going to use them again. I need the side molding for the windshield (the original molding shrinks and tears off from the wind force while driving the car). The GM Dealer out here wants $67 for each side molding - plus tax. That's a rip off.