Not sure where the GM 6.0 can't pull 8500lbs... Guess it's time to trade up...lol... The current 6.2 ford, 6.0 gm, 5.7 dodge has no problems pulling heavy loads. Years back the mighty 454 was weaker then the current gas jobs. I pull close to 10000 or higher, no issues with my 6.0. Anyway I'm sure the new 6.4 will perform very nicely, looking forward in hearing a future tow report.