I own a crew cab with the 3.73 diff. When I bought the truck, we went on a bit of road trip (800 miles) to break it in. I was extremely pleased when the lie-o'meter said 15.5 mpg. Since then, it's gotten progressively worse - around 11 mpg. I towed a trailer last week on a short haul and only got about 7.5. I had the PCM re-flashed today (TSB 10-21-13) and am hoping that the mileage improves.
My highway mileage today, pulling my tandem axle, 9000 lb, 36 foot travel trailer with a 15-20 mph tailwind was 8.1 on the lie-o-meter. I have found it to be no further off than .2/10ths of a mpg compared to hand jam figures. Still baffles me reports of owners getting 12+mpg pulling heavy loads.
I have F350 CC flatbed 4.30 gears , at 3000 miles was getting 12.4 at the most around town. I drove to Oklahoma this weekend with a polaris RZR on the back with a windshield
on the rzr, it was like having a wind dam on the back not to mention a constant 30mph head wind. I was gstting 11.7 by the time I got home, I was hoping the lie meter would go up fron 12.4 , but it didn't. Leaving for MD next week pulling a 30 ft lite Dutchman travel trailer. I'll get back to you on how that turns out.
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