37s and 3:73s

[Ehall8702]

When you go larger on tires, you won't get better mpg, it will get worse. Don't know how you will achieve 25 mpg, when I had the same setup with 3:73s and 33s and got 12.5 mpg at best.

ND a 2500 has different shift points and is totally different mpg all together than a 1500, but that's still low if it's the same 5.7l vortec in it. Same stuff applies tho, gotta have all ur sensors Workin or it defaults into a rich air/fuel mix and gives horrible fuel mileage

 

[L31MaxExpress]

My heavy ass express conversion van with full 1-ton suspension, 5.13 gears in the 10.5 full float, 4L85E with a 2,800 rpm high str converter, ~500 hp 383 and LT265/75R16s has gotten 17 mpg highway and I am still working on the tune.

 

[lubbockguy1979]

My heavy ass express conversion van with full 1-ton suspension, 5.13 gears in the 10.5 full float, 4L85E with a 2,800 rpm high str converter, ~500 hp 383 and LT265/75R16s has gotten 17 mpg highway and I am still working on the tune.

31" tire.... 5.13 gears. Out of curiosity what is your hiway speed?

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[L31MaxExpress]

31" tire.... 5.13 gears. Out of curiosity what is your hiway speed?

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Between 75 mph and 90 mph most days. With whatever the flow of traffic is moving in the LH lane. When I am towing the travel trailer I slow down to 70ish. 70 mph is about 2,850 rpm. 90 mph is about 3,650 rpm. I was on the 85 mph toll road a few weeks ago running with traffic. Cruise set at 98 running 4,000 rpm for a solid 50 miles. Still got 16.4 mpg that tank. It was running at 17:1 air fuel ratio and 52* of timing with 15 in/hg of vacuum. It is overgeared when not towing but geared perfectly for running with the trailer.