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Discussion Starter #1
Last fall I bought an 08 Silverado 3500 with an LMM to tow an off-road race truck in a 24' enclosed trailer. Truck is 100% stock with 187k miles on it.

I've gone to the local off road park 3 hours away in PA the last two weekends and have found my average fuel economy to be 8.4 mpg. I know my trailer isn't the lightest or the most aerodynamic, but I was expecting a little better based on how my 24v cummins dodge performed with this trailer. I would estimate the trailer loaded to be around 8000 lbs give or take, and I keep the speeds in the 65-70 range. The truck doesn't seem to be struggling at all and stays in 5th or 6th gear most of the time at highway speeds.

Is there something wrong or is this normal MPG for my kind of load? Would a towing/delete tune help?

 

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If you weren't running against the wind, I'd say 8.4 is low. I figure about 10MPG overall pulling my hi-profile 5th wheel, about 10K lbs. Sometimes more, if road is flat and there aren't many hills; sometimes less, hills, wind, stops and starts, etc. I have gotten as low as 6 bucking a strong (35mph) headwind. Keep it to 62 if possible and your mileage will improve over driving 65 to 70. Steady speed makes more mileage.

I bought a tuned ECM from John Kennedy and I believe that might be the difference in the mileages. I really like the extra torque and reliability that it has given me. And it makes it a blast to drive the truck without a trailer attached, something akin to stepping up from a 283 Chevy to a 327 when I was young.
 

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Added advantage in the tow tune is the turbo brake feature, especially when towing. I agree that there is room for improvement. If you slow to under 65 mph lock it out of 6th unless you have a tail wind. I will assume that you still have the DPF and that hurts some on MPG. Keep checking your mileage as more fillup are needed for a good average. Might check into an aero bubble for the front of that trailer. Do the research.
Talk to Kennedy, he knows Duramaxs and can give you good advice.
 

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I tow a 38 foot -12,000 lb 5th wheel trailer with a stock 08 GMC 3500 SRW and I average 11.0 mpg in the hills of Tennessee and slightly better that 12 mpg on level ground near sea level. I should thing you should do better than 8.5 mpg with only a 8,000 lb trailer. What are you getting without the tow?
 

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Discussion Starter #5 (Edited)
I haven't calculated without the trailer. Honestly I dont drive it enough without a trailer to get an accurate reading. Maybe I'll start driving it more to figure that out.

I still have the dpf and the tune is stock.
 

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The most efficient rpm for towing is the 1800-2000 range. Speed at 65 or under will yield best results. I lose 2.5-3mpg going from 68mph to 78mph. A good intake, exhaust and tune will help to.
 

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Is this based on the DIC avg or hand calculated?
Stock id avg 9 towing 8-9.2K travel trailer.
 

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I get around 10 to 11 mpg pulling a 9,000# travel trailer, but mine isn't a drw, and I have a canopy, which helps smooth-out the airflow a bit. I also shift out of tow/haul mode when I am on the flats, and I use cruise control. But on the hills, I use T/H and turn-off the CC.

BTW, every time I checked the DIC, it has been very close, so I don't hand-calc mpg any more.
 

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What kind of mileage did you get with your cummins pulling the same trailer? Was it a dually?
 

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Your profile is a brick now. A cap top may help some with the aerodynamics and a tune would help. An aftermarket exhaust would help too. Biggest fuel savings would come from slowing down
 
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