I get 20 + all the time inthe summer with my 99 3500 dually with 4.10 and 5 spd . I drive 60-62 mph max Over this mpg goes down fast. Even a high head wind will kill mpg. I also have gotten 17 pulling a very heavy equipment trailer over 1900 miles. We ran 55 most ofthe way. With the 4.10 daily driving especially around town is a lot of shifting but you also can run in 4 and 5th a lot at lower speed so mpg is not bad around town 18+ usually.
The one thing that does kill mpg is the winter fuel. I notice it around the 1st of Oct here in MN it gets progressively worse as winter gets colder and more fuel adjustment are added. I added a radiator block off this year and found that mpg went up dramatically. This is the first time I have gotten above 20 inthe winter. I got right on 20 when it was -5 outside. I travel about 250 miles almost every weekend over the same road and use the same pump so I am very consistant in fillups. I tried it without the winter front and got 16 no other changes!!! This is about what I usually get when it is very cold.

I do have a straight pipe which is worth 1 mpg across the board.

My work friend gets as high as 24 with his 3rd gen driving about the same. He get 15 with his 30 ft 5er TT at 55-60. He has 3.73 and auto in his 3/4 2500 4x4. stock

 

With 90k logged on Im getting 14 mpg combined hwy/st. Im running 3:55 with 33 in. tires, Edge engine controller and AFE filter on my 02 2500 Quad 4WD. That'll be the day I see 16-18 mpg!

 

im glad u posted something mine is a little older but also wondering whats wrong 1998 cummins 12 valve automatic i put about 20 miles a day on it around town. I can average 13-14 in town. down the interstate a 75 mph i can get 16. in town no matter how i drive it, its the same pulling or not. I have no muffler and just a cat. Replaced the fuel filter. Is it just the winter with the mixture between #1 and #2 i just bought it about 2 months ago so i havn't had a chance to run it in the summer.
thanks
jared

 

your mileage will go up in the summer. this winter fuel is crap[:'(]

 

thats what i like to hear!!!!!!!!!!!!!1[sm=groupwave.gif]

 

I'm in Florida - not sure if #1 and #2 are mixed here. My 2500 (2004) has 12,000 miles. I get 14-15 in town, 17-18 on the highway, and about 11 towing. No mods on it.

 

#1 is home heating fuel, I dont think that stuff is used in automotive aplications anywhere in the US mainly from a filtration view. #1 isnt filtered or refined as well as #2.

second, if you have a 4.10 rear axel then your mileage is pretty good, with a 3.73 you might need to change the air filter and fuel filter.

 

Just to state, since modding my intake for the BHAF my mileage has gone up by about a full mile per gallon. straight stop and go mileage is now at 16.5-17.5mpg. and straight highway is flurting with 20mpg.

I have noticed my truck doesnt smoke as much under hard acceleration.

 

My 03 2500 automatic has about 54000 on it. I average 65mph to work and back and am getting about 17.3mpg according to the overhead. I will say that I was getting 15-16 mpg when I first bought the truck. After 10000 miles the fuel mileage went up. Now I must say I am extremely happy with the 17.3 mpg. This is because my 99 Dakota 4x4 V6 manual was getting about 18mpg. My wifes 04 AWD Pacifica is getting about 20mpg. I feel like I made out.

 

I'm getting 20.6 with a 99 24 valve 4x4 with 110,000 miles, stock except for a MRBP 4" exhaust system. I use Drew's recipe of 16 ozs of diesel conditioner & 8 ozs of Marvel Mystery Oil with each tank.