Sumr616,
I wouldn't say GMC swears by it. That being said, I am of the opinion that if GM is going to install a monitor in my car that tells me the useful life of the oil, and I abide by it, then any problems that may come around where oil change frequency is an issue then GM won't have a leg to stand on (IMO) if that type of monitor is installed in the vehicle.
I *will* say that it depends on your service advisor. My service advisor has already mentioned to me that she doesn't recommend me going longer than 5k on my oil changes. I don't want to compare apples to oranges, but I have a Mercedes as well and the PRINTED service manual that comes with that car shows the service (including oil changes) interval at 13k. I fully intend on going by the tool/monitor that GMC has installed in my 2011 Terrain and NOT by mileage when going in for oil changes **for the most part**. I've had/having enough issues with my 4cy 2011 Terrain SLT that it may not make it in my possession to the next oil change so it may be a moot point, but that's my take on it.
I don't think you're saying there is a hard and fast rule, and I'm sure I'm stating the obvious (it depends) to 95% of the users of this forum. I mean our tires have air pressure tagged on them, the dash has a RPM meter on it and my bank tells me how much money I have to play with. All of these things are in place to keep you within threshholds. *IF* I find something in GMC material that tells me my Terrain needs to go in at 1k, 3k, 10k or whatever number and it varies significantly than what my car is telling me real time, I'm going to have to have a conversation about a monitor that is uselessly installed in my car or why documentation differs from the DIC.
Adam P. Cassidy