Last year I ran into a guy on eBay selling cheap copies of the Snap-On GM Electronic Parts Catalog (EPC). I can't say if the guy was 100% on the 'up and up' as far as copyrighting goes; but I figured if eBay let him slide, things must be legit on some level. Anyhow, he charged me $50 for the 2012 install discs and one license key and they work great. This is the same software that the GM dealer uses to look up part #s and exploded diagrams; it goes back to something like the 1985 model year.
Now...to the point of the thread, the guy just hit me up to let me know he's got the 2013 version available; $50 + free shipping.. If anyone is interested PM me and I'll shoot you his email address.
It's basically the same images and information that you can find on dealer sites like this:
http://parts.nalleygmc.com/default.aspx , but you'd have it on your own computer.
Here's some samples of the quality of diagrams the GMEPC has...and it covers all GM models (Chevy, GMC, Hummer, Cadillac, Pontiac, Saturn, even Saab)
