I could have kept my gasser!! 90 gallons of fuel from Wisconsin to Mammoth Cave KY, and I have some left in the tank, but not much. The auto trans kicks down and stays unlocked for MILES and MILES and that really sucks down the fuel. I got better mileage running 73 because the trans can't unlock or it will redline. At 65 it unlocks at every hill and stays there until I give it a little more juice and then let off to lock it.

I think some type of trans chip or trans work is in the future.

7mpg pulling 10,000 lbs....

 

I bet you have a auto dont you?? Mine is doing the same thing.

 

If you are towing 10,000 lbs uphill at 65MPH what do you expect? At some point it has to downshift. I don't see how all your mileage complaints can be caused by simply unlocking. 10,000 lbs in the mountains is the bigger problem. Am I missing something?

Wetspirit

 

That is pretty bad, my 06 gets around 13 to 14 pulling 8000 lbs and the best ive gotten is 16, and i live in Northern BC Canada in the mountains, your either going up hill or down, mine is an auto also, I try and tow at 60 to 65 mph, anything over it sucks fuel.

 

I just drove down to Utah 2day, 60-65mph, head wind the whole way pulling my Jeep and trailer (7000LBS) puter says 12.5...used the cruise 90% of the way and I didn't really notice it dropping out of lock except for a couple of long climbs, I was more worried about the EGT's

 

I'm pulling a 14,000lb 5er and I just got about 11 to 13mpg. There's a few 6% grades along the way too.
I found it best to run 55 to 62 mph while towing, I'm also running with 4.10, so you would think I'd be down even more on mpg. The truck has a nice sweet spot at about 2200rpm in tow mode, and anything flat I turn TM off.
I do play around with the throttle a little to get the tranny to kick-in out as needed.
I have no complaints with my stock 5.9.

Just started the install today of my Jake Brake. It won't help my mileage, but it will be a good addition to the truck.

 

I pull 12000 lbs daily get 12 - 14 with my auto.. ????

Shane

 

I got 10 mpg pulling 11k over 1000 miles at around 70 mph. I was disappointed in that.

 

10,000 lbs in the mountains is the bigger problem. Am I missing something?

Wetspirit[/QUOTE]

2nd that! But i too pull about the same weight (mini excavator) in the mtn's of east Tn. and don't get that bad of milage. Mine is usually around 11mpg pulling that kind of load

 

I'm with u my 05 sucks down feul when towing and empty. I do tow heavy like 12-16k and in flatish areas around 50mph i get 8-9 mpg. I wish I had the 3.73 my other truck had. My 03 got 20 highway and 10-15 towing around 12k. It also did not have the power the 05 has so I guess you have to pay to play but I wish I could get it up a bit though.

 

3.73s dont help either! GCVW of 21.5K-23k I get 9-11 MPG running pretty much any speed. I usually try to run over 62 to get the RPMs right.

 

Lost Lake it really sounds like something is really out of wack on your setup. I have towed my boat (#6500) to Kentucky & Lake of the Ozarks and worst was 11.8 mpg the best was 13.7 driving mostly 70-75. Hills were not even a little problem on tow/haul at the time and never searched gears like you described. My truck had about 10k miles then. I will assume you were using the tow/ haul and OD lockout correctly. What about the air & fuel fiters , I change the fuel every 15k and air when it looks dirty. The fancy thing for the air filter has never moved on mine. I have read where some folks lost their boost because of hose clamps comming off. What about your transmission level, is it ok? Your transmission could be slipping, have it checked out. Are you positive your trailer is pulling ok, brakes not dragging, axles not hot. Hope this gives you some places to look at.

 

Mine is getting worse. I am have tranny trouble and I beleive all of our bad fuel miliage is coming from the tranny slipping. The power isnt reaching the ground.

 

I just read the post on towing/rv the same topic as here.https://www.dieseltruckresource.com/...d.php?t=142669

 

If I was towing that little weight 10,000 lbs I would expect my truck to speed up to 80 by the top of the hill
Why does it have to downshift??? What am I missing something??
Lost Lake how many miles on the truck?? My mileage was around 6 starting out and now I am at 9-11 depending on speed and wind. and thats being at 34,000+