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mpg increase after break-in ?

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I have a 2015 hd3500 dually 4x2 6.0, stock rear gear, (3.83 or 4.10?) the gvw is 13,200, i have a catering truck body mounted and fully loaded, with me in it, weigh 11,800. first 500 miles was averaging 7.4mpg, now getting in low 8's with a 11.4 as best. set for every 40 mile refresh. I know have 1200 miles, can i expect better mpg as motor breaks in? or is this it ?

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My 2015 Silverado 2500HD 4x4 Duramax with 3.73 turned in 11.7 mpg avg on our recent 2000 mi trip through TN-KY-WV-VA and that was hauling a near 40' 5th wheel weighing near 16,000lbs.


The Duramax has just over 8k miles on it now and that was with a lot of mountain driving/hauling so I am hoping it will get even better...

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  • 2 weeks later...

We have a 2014 LML Duramax in the family and running empty bed but 5 adults in cab @ 65 - 70 mph on a 600 mile trip I saw 20 - 23mpg and hand calculated a solid 21 at fillup.


Towing a 2 snowmobile covered trailer in the mountains (which weighs ~ 2000lbs loaded) got 16mpg @ 65 -70mph.


Towing a 4 snowmobile covered trailer in the mountains 7,000 - 12,000 ft (trailer weighs 7,000lbs loaded) got 12mpg @ 65 - 70mph.


The 6.0 is known for being thirsty but it is a proven workhorse. The LML is also a great proven diesel.I would say your 6.0 mpg loaded seems normal and won't hardly increase (maybe +1 mpg) after break-in.

Edited by 2009 GMC
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