Yea, for the most part most guys are happy.. You'll see a emissions component failure from some, a few major issues from others.. but most are happy overall. That's pretty good for modern diesels these days, as emissions have haunted most diesels.
Agree.. It's usually pretty close most of the time. But the manual way never lies! I use fuelly as well.. works good and give you a good sense of mileage over time.
Likely not, but the dealer also drives that conversation a lot it seems. However, If you have a catastrophic issue don't be alarmed if GM rep comes down and points to that, when in fact it's 99.9% chance the part/mod has nothing to do with the failure.