Fuel mileage?

I have a 97 dually powerstroke and I'm looking to improve on this 14.3mpg.
It has 4.10 rear gears in it now and I know it will improve with 3.55's
The question is how much is too much I have found 3.08 and 3.31. I don't use the truck for much
More than a DD. Just trying to figure out where the higher gears will start hurting mileage.
Any thoughts?

I wouldn't go past a 3.55 . I put a 75 HP chip in mine and picked 3mpg

I put 3.73 gears in my 95 crew cab dually and an edge programmer and both helped. it was a five speed truck.

From what I've seen with 4.10's they get around 14.
With 3.55's they get up around 20. I would probably be
better off just trading it off but 4 door F-150's don't seem to get
any better. And it's paid for I was thinking of trying the 3.08 just to
see how it would do.

I have 3.55s in my 1993 f250 7.3 it not the powerstroke in is the idt but I get 20 mpg with a 5 speed with the 3.55 but if you are not driving long distance you may not see that much of a mpg change as the 3.08 might lug it much around town.

I have 3.55 gears in my 97 ext. Cab 2wd Automatic,powerstroke. Tony wildman chip, made my own Cold air intake.I average 17 mpg in town and 22 mpg on the interstate. I got 13.8 pulling my camper on the last trip. I love the 3.55 gears.

Mine has 4.10 gear and a 5speed ,it get about 18 running around here ,but on the interstate it drops to 15. It's turning around 2500 rpm at 70 mph. I think a 3.55 would help it?

There is a fine line finding that sweet spot where an engine is it's most efficient, and IMO the 3.08 gear is way too much and the engine will be working like a dog under the power curve to keep that thing going. I had a 97 P/S CC with 4.10's and it did about 16mpg, moved up to a 99 F250 with 3.73's and it would do about 18, 02 Excursion with chip was about the same with the 3.73's. Buddy had a 96 P/S with 3.55's and he was upper teens all the time. I would do the 3.55's if it were mine.

I just swapped from 4.10s to 3.55s went from 14 around town to almost 17 and on a tank of half town and half interstate it got over 18. I never got over 17 on the interstate before with the 4.10s no matter how I drove.

I'm expecting over twenty on the next interstate run, 97 4x4 short bed 4 door F-250 Baby Swamp injectors an a six position chip.

If you pull anything heavy I would not drop below a 3.55 gear. The injectors and chip made this truck a totally different truck, it's very enjoyable to drive now.

Heck put some HHO on it and you get a 25 mpg won't it

Honestly my thinking was to put the 3.08 in and kick the od off on the short trips and then kick it back in for the interstate driving. I'm going to check some gear cal. to see where it would be at 60 and 75 just to see where they would put it. I've got a buddy that told me he'd let me try a set of 3.55's when he took them out next month. So I may just try that.

With a 33 inch tire you will be around 64.76 mph with a .77 O.D. @ 1800 and a 3.55 gear.

At 1550 it will be about 64.42 mph with the 3.08's You will be out of over drive in a stock 7.3 pulling.

My feelings are that if you get the cruise rpm down to much fuel mileage may start to go the other way, you fall out of the efficiency range of the engine.

There is a huge difference in 4.10's to 3.55 's I thin you will like it.

The sweet spot like Schmitty talked about is the ringer.It has alot to do w/Tire size,Tranny,and gear ratio.AND if you are gonna be towing and how much weight. Mine had 3.55's w/33" tall tires..Bought my HEAVY 34' enclosed and it would not stay in overdrive EMPTY. Switched out the gears to 4.10's and it actually picked up from 17 to 19.5 mpg w/o trailer. And now it stays in overdrive w/loaded trailer. Your results may differ.