[OverBoardProject]

I agree with you DM, but if they figure that they can say you never greased the truck or it looks like you were hitting curbs they'll reject your warranty.
GMC will never take their franchise away if that's their argument.

The best way to not have warranty problems is to take it into a shop for service. It doesn't have to be the dealership for the service, just a shop. Then you've got a record of the mileage when everything is done.

For the DIY people out there the dealer will often expect you to use only GM replacement parts for the warranty period. Again so they can roughly calculate if it's done during the recomended periods.
The biggest thing here is if you've gone 15,000 miles and your suposed to change the oil every 3,000 miles they want to see that you've bought 5 oil filters from them.

If you figure that something should be a warranty issue and the dealer still hands you the bill telling you to pay that's when you should really ask for the parts.