Unless my math got mixed somewhere. I had a CHP buddy clock me when I was doing what the truck said was 70mph, turned out I was doing 76, plus 10%, so then I knew my trip meter was off by about 10%. I get a little over 600/tank and I've never put more than 32-33 gallons. Given the differences in reading I'm really getting 660/tank which is 20mpg/33gal. I also tend to do a bit of drafting when I can, never dangerously close though, 2-3 car lengths.

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That wasn't a 1 tank average either, that was over the course of 5 tanks going from Ventura, CA to Little Elm, TX and back, a total of about 3000 miles. I've always noticed MPG will kinda spike right after an oil change too.

the BEST ive done was 17.6(hand calc.) going 60-62mph..... IF i ever saw 20mpg at 70mph id shit a brick

No no no, I didn't average 20mpg at 70mph, we just used 70 as the test speed to see just how far off my speedo was. TX and back was an average of 60-65mph the whole way, 55-60 on the speedo.

Diesel Daddy, how are you filling the tank? Just filling it up til the pump clicks off? That's probably why your numbers are skewed.

x2, i know mine is accurate cause i fill it till its about to spill out, going til it clicks the first time is NOT accurate

It's most of the reason I don't even check anymore, never had the patience to sit there slowly filling for 15 more minutes to get it to the top. However, it is the only accurate way of calculating mileage.

Unless you drop your tank and do the harpoon mod!

i used to check all the time, but like you said its kind of a pain in the ass... now i just drive, if i was worried about mpg i would not have got a truck... now i think i get 10-11mpg cause of warm ups and i drive like i want.(FAST)

In that case I'm down around 17/18ish hwy, which still ain't bad

That's actually still pretty good. 18mpg in a truck this size and of this weight aint nothing to shake a stick at brother! :c:

Thanks guys for all your replies I think today I'm going to go Down to the ford house a try and pick up a 07 f-350 lariat 6.0 hopefully can talk them down more lol I think it's time to go back to my ford roots and sell the dodge I really really like the cummins engine cause for 100k miles the only prob I had with it was a lift pump. But now the truck is getting 13mpg when babying it not using it for its purpose and that's just not going to cut it. Well thank you all for all your input I'll post pics and updates later.