[JRTJH]

I'd suppose that your Chevy dealer has installed one or two hitches in the past several years. That doesn't really qualify them to be "experts" in drilling the holes. It doesn't mean they can't, but they really won't have much experience.

To compare, do you want someone who is an expert in diagnosing heart disease, but hasn't done heart surgery in the past 3 years doing your surgery? Or would you want someone who does heart surgery every day???

Chances are the hitch installer/hitch dealer in your local area has installed more hitches in the past 6 months than your local Chevy dealer has in the past 6 years..... If it were me, I'd choose a competent hitch installer to do the rail installation and let the dealership take care of warranty work and oil changes. YMMV