The extra gear ratio's over the six-speed make it much move flexible in the mountains, especially going down hill where "Grade Braking" down shifts as required to hold the speed back to whatever the cruise control was set at. Really saves on brake pads.
I just checked the 2016 Silverado User Manual maintenance section, and there is no mention of this "complete tear down". It is hard to believe that GM would build and people would buy a truck that needed a complete tear down every 25k.
I would love to hear from anyone who has actually had a "complete tear down" at 25k.