not nearly enough. I put a 16 gal fuel cell in my bed and itll suck through it in NO time. next time i fill up ill log the millage and try and figure it out for you. If i had to guess like 8-10mpg? maybe more if i didn't get on it all the damn time haha

 

Hwy - 18/19mpg
City - 10 mpg

Estimated HP - 530

 

you know, 10mpg with 500+ hp isn't bad. esp the 18/19 part. I get about 16 mpg city and only 20-21mpg (not a big difference from you) on the highway depending on the sustained speed, i get better mileage if i stay below 70mph than when i do 80mph, obviously, but it doesn't make a huge difference. I have the getrag (which will be traded for a t56 soon) which has the same gearing as the NV3500 for 1/2ton trucks, which is 0.74 5th gear.

What type of transmission do you have in that truck?

 

700R4 with a lockup converter

 

i have the nv3500 now and i been puttering around town with it recently and ive noticed a huge improvement on gas millage although i don't know exactly what it is, but ive driven a lot farther lately on just a quarter tank than i did before. prolly had something to do with my timing being off and my carb not being calibrated right, but now all is good.