I have an 03 6.0 tuned. Trailer is 35ft and weighs in at 13k. Total truck and trailer weight is 22,300lbs. On our last 1300 mile trip to Maine and back I saw an average of 9.5mpg. Now there was a lot of hills so I am hoping to see 11-12 when I head out west on flat roads.

 

I use it to make sure I have enough money in the budget to make the trip.

 

In terms of terrain, towing our fiver with our 7.3 going from hill country of Appalachia to the flats of Florida give us a .5 mpg bump maybe. I don't think it ever changed it more than that. Usually mpg hangs in there at 10.5 - 10.8. I do back out of it on the biggest hills though, when downshifted, and do not try to hammer down regardless. Mostly I watch my EGTs.

Steve

 

My 2002 diesel with camper is real consistent at around 11.5 mpg anywhere in US east of Illinois. As I head west of Illinois my mpg gradually drops with every fill up to about 8 mpg and then climbs back up as I head east back to normal. Anyone seen this?

 

Yes, in our '06 5.3l gasser we see an increase in MPG as we go East from California and get the crummy fuel out of the system. Kinda funny in that as we go East there are a lot of mountain passes, but our mileage increases. Next summer I may be able to tell F it changes with the diesel.

For the OP's question, I do see about a 4+ drop in MPG towing vs unladen in both trucks.

 

My first trip with my truck. 27' Salem by Forest River. I got 9.4 after recalculate for bigger tires and I was in some very hilly terrain. I was hoping for better. But my buddy in his '11 with the 6.7 psd got 10.8 pulling a very similar load, so not bad overall.