Severe gas mileage issues. My 2019 with same 6.6L engine got 26mpg hwy 19 mpg cityand had 8 speed trans. Brand new 2021 2500hd diesel gets 16mpg hwy and 13 city with the 10 speed Alision. Seems like it doesn't go over 6th gear. I tested with rpm gauge at 60 mph on flat highway in Drive. Dropped shifter to manual and it's in 6th gear not 9 or ten. Also downshifts at speed when foot comes off throttle. Dealership today put on computer 45 minutes, No Codes. Hopefully someone can respond with help. 2800 miles and only trailered a bass boat once at 14 mph hwy. Ugh
Jamiecoyle21
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