drove 50 miles between cities about 1 percent maybe 2 grade with 30 mph headwind pulling 15000lbs and got 4.7 mpg. that sucks! not really any better then my gasser as far as mpg but could easily pull it faster.

Had to of figured it wrong...that really does suck!

How many miles on your truck? Mileage did not start improving on mine until 15K miles.
What speed/rpm were you traveling at? Above 70 the mileage starts going down.
Was that hand calculated or the DIC? The DIC has always shown low on my truck.
Did you factor in the 265's? If not you were actual going farther than what the odometer showed.

Going through Montana on I-90 against a strong head wind empty I got just under 10 mpg so with 15000 lbs I can see how that might be. To bad you can't tack back and forth like a sail boat to use the wind instead of fighting it. I forgot to mention that was in my 2001 F250 PSD 4x4 Crewcab.

12500 miles, hand caculated foot to the floor doing 65 mph. i normally average 9 pulling this trailer.

12500 miles, hand caculated foot to the floor doing 65 mph. i normally average 9 pulling this trailer.

30 mph winds is a lot. No doubt that is what killed your mileage.

I would get that truck into the shop pronto...I pull a 30' fifthwheel from California to Colorado and have never been under 10.5 mpg on the dic, and hand figured it was closer to 11 mpg (10.8666 mpg actually).

ive asked several dealerships about milage and they all say the same thing " cant do nothing about it". ive never really got more then 13 even when epmty so i am lost as to what to do.

FYI, My 05 @ 3k got between 5.9 and 8.9 pulling the fifth wheel @ 72MPH from WI to FL and Back all hand figured. Truck now has 6k and was 9.2 @ 58 MPH with a lot of little towns in the hauling mix. I hope it gets better and my 2500's all get from 14-19 empty and the 01 got avg of 10 MPG pulling the same trailer @ 75 out west. I am heading out the end of the month to see friends in WY and We'll see how that go's, MPG and the run's hot issue.

It may be your alternator working so hard to try to power all the extra stuff you have listed in your signature.

Oteo125 ... Your oversize tires probably hurt your milage somewhat in this situation. Also, have you recalibrated your odometer for the larger tires? If not, you are displaying less miles than actual, which will result in an inaccurate lower miles per gallon result after doing the hand calculation.

Towed my FifthWheel for the first long trip last weekend. FW weighs around 10,000lbs. Truck has 15,000 miles. 700 miles round trip, 350 miles freeway @ 70mph, 350 miles highway @ 65mph. 10.6mpg getting there, 9.6mpg getting home (windy conditions). Tranny temp stayed around 190, occasionally drifted to 200, engine fan came on several times during the trip but engine temp stayed around 210, saw 230 a couple of times on long grades, but fan cooled it back to 210 quickly. I was hoping for 12mpg or better, but I was very happy with the power and stability of the truck.

the 4.7 is almost believable. a fiver into a 30 mph headwind uphill! that is the perfect storm. i have a tall cargo trailer, and i have found out that wind is everything. i have never encountered a 30 mph headwind, but i had some stretches into 20 mph'ish headwind with a 9k pound trailer and was in the 7's for mileage (note bigger tires - odometer adjustment accounted for).

but... what seems crazy.... is 13 while empty. that seems like something is not right.

it goes to the dealer tommorrow for a reflash and for them to check milage. ill let you all know what happens.

the dealer amitted that it should get better milage and that there is a bulitin out on poor milage from gm. thay didnt tell me much more other then they needed to keep it another couple days. the best milage ive gotton was 13 to 14 and that was driving like grandma. can i claim a lemon if they cant fix it due to milage? i want to keep the truck but the milage needs to be fixed!

they said everything looked fine and they reflashed it. drove a little today and everything is the same with mpg. gonna give it a little while and take it back.

If I recall, my 265s shaved off 1 mile for every 25 driven, which would be 4 per 100, or 4%. I could not tell any difference in mpg between the 265 or 245. Keep in mind that your towing test was in the "perfect storm" as mentioned earlier. What would the mileage have been if you drove back with the wind to get a "true" reading. Kind of like having the DIC on instant mileage and putting it to the floor. That will show poor mileage! But I agree, your empty mpg does sound low. My foot is plenty heavy, and I will get at least 15-17 empty. 18-20 if I take it easy under 65 and in good conditions.

Welcome to the club. I dont doubt it at all. And trust me GM pleads the 5th on any complaint concerning fule mileage. They dont have to report it you know. It could get 3 or it could get 30 its all good to them