I have an '09 2500HD/3.73 and I am towing a '97 Excella. Trailer weighs in at around 7900# I avg about 8.5-10.5 depending on conditions. I leave it in tow/haul and run about 60-65.

My toughts are that you don't buy the 6.0L for the fuel mileage, you buy it for the torque. I pulled a friends '54 Cruiser and avg 11.5-12.

Along with the K&N, Royal Purple HPS Motor oil and Lucas fuel conditioner. It will give you about 1.8 to 2.5 more mpg. The lucas fuel additive is cheaper by the gallon(around 30). I prefill my own 1/2 pint bottles for use during refills. Love the stuff.
Try it once and see for yourself.

I have a 2500HD with the 6.0 and 4:11 rear. When I bought the truck my research showed people were getting better mileage with the 4:11.
I will lose 1 mile per gal for every 5mph over 55mph I drive. Also I will lose 1mpg if I use 10% ethanol. You wont gain anything if you use premium gas as the 6.0 is a low compression engine. Driving into a headwind will also kill your mileage. Use high quality lubricants in your diffs, transfer case, trans, and engine.

I drive a 2007 Chevy Avalanche (1500) 2wd with 5.3L and 3.73. I am a pilot so I am constantly monitoring anything that can be monitored and in this case, fuel burn and trans temp are about it. When I first got the AS back in Dec, I was shocked to see my truck go from a highway average of 20 mpg all the way down to more like 8.5 once hitched. This terrified me. Since then I've towed 2500 miles and much to my surprise the fuel economy has steadily increased to where I now average 11 mpg. * I live in the south where it's mostly flat.

Nothing about anything to do with my setup has changed at all over this time except the total weight of the stuff we bring with has gone up. Something that should have the opposite effect. The fuel economy does not seem to change if I drop down below 65 nor does it seem to go down if I go over 70... I've never pushed it though to find out.

I'm very happy with my TV and Airstream's towing capabilities with one exception... in hot weather, stop and go traffic the trans temp gets up there to 210 degrees. The manual says 180-205 is normal operating but it give no other limitations. Should be interesting to see how the setup does over the mountains this summer!

Fundamentally, it takes "x" amount of energy (btu's) to move your basic Airstream through the air and down the road. A little more for bigger, wider and a little less for shorter, narrower. Some engine/transmission combo's are a little bit more efficient than others and, of course, diesel has more btu's per gallon than gasoline.

Still, it takes more or less the same energy. So, if you surveyed all who tow, I'd be willing to bet that, long term and on average, most of us driving gassers are averaging 10-12 miles per gallon.

If you budget for that, you will seldom be cast into despair and may occasionally be delightfully surprised.

Mike

Our 5.7L Dodge does real well at 13.8 to 14mpg running flat ground with no or little wind at 60 pulling our Overlander.. But throw a 25mph corner wind at us and push it up to 68mph it can drop down to 11mpg in a heart beat..

Now here is my beef.. We have a well worn out (800.000 miles) 94 KW semi,, pulling a 42 foot grain trailer.. Several years ago I was pulling dry fertilizer out of Tulsa Ok.. 79,500 lbs total weight.. It was a nice day with little traffic. I just idled along at 50 to 58mph and made a 550 mile trip at 9.8mpg.. Never let the turbo boost go over 10lbs and roller coasted the hills as much as possible. I understand we are not matching up apples to apples but that rig is huge in relation to our A$..
By relation to profile and weight,, our TV should see 28mpg all the time..
Sodbust

Thanks for the input , I presume you have one of those conventional KW tractors with the sloped nose front end . When those first showed up I thought they were terribly ugly , but after driving a few of em and comparing them to the old 68 cab over KW with a 335 Cummins inline 6 and a 13 spd I broke out in , that ugly front end does help with wind resistance . The old 335 would get about 5 mpg in the mountains of Wyoming and Utah pulling a float and grossing a bit less than 80,000 . And would hardly do any better running empty !
Much the same for our Dodge 2500 with a 5.9 Cummins inline 6 with a 5 spd overdrive on the back of it . It gets 14 to 15 mpg pulling the AS with all the usual stuff loaded and fresh water tanks full . And only a couple of miles better running unhitched with no load at all.
Weight has much less of an impact on the MPG of a long stroke high compression diesel engine with a manual transmission than it does on a low compression , short stroke , gasoline engine coupled to an automatic transmission .
We used to pull the 66 AS with a 1971 International Travelall with a 393 V-8 coupled to a Chrysler 727 slush box with a 4.10 rear end , back when the speed limit was 55 nationwide and got between 5 to 8 MPG.
All these modern computer controlled gadgets that are on newer engines have defiantly helped with the mileage and power , but at the heart of the engine is still a low compression reciprocating piston gasoline engine .

Here is my approximate experience, 08 Silverado 5.3L, neutral wind, etc.

60 MPH 11 to 12 MPG
65 MPH 10 to 11 MPG
70 MPH 9 to 10 MPG
75 MPH 8 to 9 MPG

My other TV 04 Tahoe 5.3, is the same less about 1/2 MPG.

Driving habits come into play a lot. I try to hold my travel gear with minimal downshifting, modern cruise control sucks while traveling in hilly terrain, it drives me nuts and wastes gas.

My goal is to NEVER allow a downshift above 70, the cruise sucks at that.



1/2 Ton 4WD Truck, 72 Sovereign Hensley Arrow

I emphatically agree. Was really surprised how "stupid" it is and disappointed that it's almost unusable. It makes long trips even longer. I've been very surprised how mentally drained I am when I get to a destination after towing.

I only use cruise control on flat stretches just long enough to move my right leg around and stretch it then its back to manual driving.

Kelvin

I have a 2002 Safari 25. I have owned a 2010, 2013, & 2015 Chevy crew cab 2500 with 6.0. 3.73 rear end until 2015. 2015 has a 4.10. My normal average on trips in excess to 1000 miles is 8.5 mpg. Short trips will vary some.


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Not a total surprise. I used to tow a 6,000 lb 27' Safari with a Chevy half ton van. 5.7 liters with a 3.73 axle. Tow vehicle was not rated to tow in OD so I towed in 3rd. Mileage was between 11-13 mpg at 60 mph. Considering I went to a 3/4 ton GMC van with a 6 liter gas 4.10 axle and now pull a 30' Classic slide that weighs about 8,600+ lbs (depending upon how much fresh water I pull). That vehicle does the same 11-13 mpg. I attribute that to the fact that the transmission on this van is rated to tow with OD (as long as it isn't hunting).

The big difference however is solo city driving. That half ton did about 17-18 mpg where my 3/4 ton is still 11-13 mpg. I pretty much attribute the betterment with the half ton is the axle and OD driving.

Jack

What I love the most is driving away once the trailer is unhitched. The truck thinks it's a Corvette and feel like I'm driving one.