I have an 04.5 ext cab 2500 Duramax 4x4. 305 50 20 Nitto 420s (not a crazy big or heavy all terrain/mud tire). Straight piped, egr delete, edge programmer. I get 12 mpg towing (very happy with this) and 16-17 not towing. All hand calculated numbers on different tunes except stock. I drove light footed to get the best numbers possible.

My question is, where do these 19+mpg numbers that people talk about come from? I had an 07 5.9 dodge with the same set up and best I saw out of it was 17 also.

My boating season is over so I figured this might help entertain some people including myself.

They are all pretty much full of sh*t....

Pretty much..

But keep in mind that with your rolling mass (tire and wheel) you have changed true gear ration and rolling resistance. The add-on edge are designed for when you tip in the throttle to increase fuel load for power (that's where diesel's make there power).

I see a mix of claims but from my experience a bone stock pre 2007 gets 12-14 pulling 8000 lbs at 65mph. 2007 -2010 are less for reasons of exhaust injection to clean the cat but the 2011 up seem to be better with the diesel emission fluid system.

Sound like your in the ballpark even with your mods. Pretty good!

I can get 20.5 on the highway running 70-75mph. But I avg about the same 17 mpg. I have '06 duramax with 4" straight through exhaust and Ppe program and 285/75-16 Michelin a/t

Keep in mind you are running more miles than the odometer is reading with the bigger tires. You changed your gearing. You can set the edge tunner for tire size but not sure how to do it to the fuel usage in the truck but you can do it old school style

My 2008 Southern Comfort Conversion with 35 x 20 Toyos got 7-9 towing and 11-12 empty in stock form. I deleted the DPF, blocked the EGR, added a MPRP down pipe and exhaust, EFI Live tuning with the CTS monitor and got it up to where my 05 Duramax was stock. 11-12 towing, 15 - 16 empty.

I love how the hippies in the epa make us burn more fuel to get a cleaner emission . My 2015 burns more fuel than my 2001. With the high idle and exhaust filter bullsh it

my 04' duramax with 265's, PPE (changed tire size and power lvl 2), fuel pump, 5" exhaust will do calculated 19 - 19.8 (~70mph) on highway... towing 19k back from Ozarks into Illinois calculated at 9 mph (~65mph).

That's impressive. Nauti Hoff

I changed it.
Good thing to think about though. Stock tire height compared to current is about 1.5". Do the math and that makes the circumference of the tire 5% more. Long story short, the distance you actually drive will be 5% less on your odometer making your mpg look worse than it really is.