Breaks grinding on 2003 silverado

Help.
I have a 2003 chevy pu, with 39k miles on it and today it started grinding bad on the left front wheel. Sounds just like a pad worn down to the metal. So bought pads. Pulled it apart. and the pads (original gm) are thick. The inside, seems to only be wearing on about half of it, and the pad looks cracked.

Is the caliper sticking? How do I fix it? Clean up the pins and regrease? Put on new pads anyway?

Or.....
Take it back to the dealer.
Not sure if this is under warrenty or not?

I have driven chevy pu trucks since 1991 and never had breaks go this fast........usually 50k miles.

Any help would be great.
Ron