Here's the scenerio: Towing 9000lb 5th wheel with 3000lb boat tandem. Highway all the way for 400 miles. Cruise set AT 63 mph. Truck is stock except Superchips programmer set on TOW. I got 8-9 mpg on trip up with Superchip on. Without chip my mileage went down to 7.3mpg. Last year made same trip with about a 1000lb less boat and averaged 12-13. I did change tires from 245's to 265's. All air and fuel filters have recently been changed. Is this about the norm with this much weight. I have got as high as 16 mpg with just 5th wheel. Any suggestions are greatly appreciated. Thank you. Truck is regular cab long box 4x4 LLY.

Here's the scenerio: Towing 9000lb 5th wheel with 3000lb boat tandem. Highway all the way for 400 miles. Cruise set AT 63 mph. Truck is stock except Superchips programmer set on TOW. I got 8-9 mpg on trip up with Superchip on. Without chip my mileage went down to 7.3mpg. Last year made same trip with about a 1000lb less boat and averaged 12-13. I did change tires from 245's to 265's. All air and fuel filters have recently been changed. Is this about the norm with this much weight. I have got as high as 16 mpg with just 5th wheel. Any suggestions are greatly appreciated. Thank you. Truck is regular cab long box 4x4 LLY.


Headwind maybe? The 265s change your odometer as well. I would say 13 mpg would the very best you will see. 16 mpg with 9k behind you is impossible. Are you hand calculating your mileage? Were your conditions different this trip? Bad diesel can be a factor as well.

I also haul a trailer / boat combo, best I've achieved is 12 Imperial mpg, in perfect conditions, usually closer to 10. Your gallon is smaller, so you shouldn't get as many mpg. I also find it hard to believe 16 US mpg towing 9K.

I don't see a problem.

5er, Boat, 265's, & Superchips = 8-9 MPG
5er, Boat, 265's, no Superchips = 7.3 MPG
5er, smaller boat, Stock tires = 12-13 MPG

That all seems pretty reasonable. No tuner = less mileage. Bigger tires = less mileage. More weight = less mileage.

All my figures were hand calculated. My 16 mpg was all under 55 mpg and very easy driving. That only happened once. Thanks for all the responses. Just double checking to see if these were normal mpgs hauling heavy. Brian

With the tire change you need to add about 4% more mileage to your trip before you divide to get your total mpg. Unless the superchips corrects this for you.