I, Know this Post is old, but Just some FYI to pass on about Chevy/GMC electrical issues. I have owned a number of Chevrolet Trucks from the Suburban, Silverado's, Avalanche, and the inline 5 Colorado. I'm also looking at a 2016 Duramax Colorado but doing much research prior to purchase.. This may help with those of you experiencing odd or intermittent electrical issues with dimming interior light, too include the infamous burnt out parking light or day time running light, and blower motor connection melting etc.. Which these problems spanned from my Silverado, Avalanche and Colorado and always turned out to be terrible grounding points.... Anyway simply put; check all the negative post connection points under the hood on the fenders and inner and outer firewalls. These posts host several negative lugs or terminals and they use a flat plate that bites the metal when the bolt is tightened. The problem is these are normally added after the chassis and body are painted and make a good enough connection thru the paint and primer, only to pass a quick quality inspection in the plant. As the vehicles sit on the lots and are driven in the weather a bit, the connection corrodes on the small areas of contact and build up resistance or may cause intermittent connections. Solution: Remove the negative posts and thoroughly remove the paint down to the metal surrounding the bite plate and or post or replace with a new one if badly corroded. Thoroughly clean all terminal lugs to the post or replace the lugs if needed. use light dielectric grease between the exposed body metal and the post plate or washer, and re tighten all the lugs back into place. Use liquid tape to seal the whole post and terminal lugs to include any exposed wires on the lugs. I forgot to mention, that if any of the negative wires are hardened from over heating resistance or corroded as well, consider replacing the whole wire, or at least cut it back 6 to 12 inches, to a softer or non corroded point, and re-splice with an environmental splice. I have found that by finding all my chassis or body panel negative posts and cleaning or repairing them, it has solved "intermittent or high resistive electrical problems. Hope this helps.