I work at a Chevy dealership and we sell a ton of 1500's. You're right about choosing a good dealer - truck or tractor, same can be said.
Your 1500 looks good. I've been eyeing a Colorado myself as I have a 07 Silverado 1500 and it's always seemed too big for me and my needs. Good truck though.
As for DEF issues, yeah I've heard about a few on the DEF sensors. My advice on buying a diesel though is to make sure your dealer has a couple good diesel mechanics. Our dealership has an excellent mechanic, but only one. It's a good thing the guy doesn't take vacations - heh.