I have an 04 F250 with the the V8 that I use to tow my 88 play-mor fifth wheel with. Right now my truck is stock and pulls it fine as the trailer is only 5k unloaded. In the next year or so I'm thinking about getting a bigger/newer/heavier 5th so I'm looking at ways to be able to keep my current truck. As much as I like to slap one of the brand new V8's in it's looking like the most cost efficient rout will be regearing from the 3.73 to either 4.10 or 4.30. So I know it will give me more pulling power but what will it do to my MPG assuming everything else stays stock? (stock tire size, no lift. etc etc)

 

My 04 F250 CC 4x4 with a 2" lift (stock tires at the Moment) V10 w/3.73 gears gets about 13-14 mpg, My TT weighs in about 7000lbs and drops to about 9-10 mpg when towing, I know you have the V8, hopefully your getting better mpg then i am, but just wanted to throw out some numbers for you.

 

i have 4.30's and i get right around 13 around town, almost 15 on the highway. towed my buddies boat last summer to lake george in new york doing 70mph average and got around 12mpg from south jersey to lake george new york

 

do you really? I have 3.73s and i barely get 13 on the highway..

 

That's better then what I get with the 3.73's. I get about 14mpg in mixed driving. (small towns with not alot of traffic and interstates)

 

From all I've heard, I doubt you will even notice a difference in mpg between 3.73 and 4.30. May even see a very slight bump UP in towing mpg.
I wouldn't invest the time and effort on the little bump to 4.10's... 4.30 is the minimum you should consider. Depending on size of RV, 4.56 may be better for you.

 

I'm going put this out there, you have an F250 with the 5.4L V8. You didn't mention Cab, so I'll assume Supercab for this purpose. You tow a 5K trailer now, and looking to go heavier, well how much heavier?

Your truck has a 13.5K GCWR, that's set in stone an axle gear swap won't change that number. Your SC towing config is 7100# with the automatic. Lot a whole lot bigger than what you're current trailer is empty along with passengers fuel, etc.

You will see mileage drop with 4.30's, but it won't be as bad as when you are towing now. The lower gears tend to shrug off the weight better. 4.30's are the minimum you'd want to convert to and see any appreciable difference. But if you're serious about getting a much heavier trailer, you may want to get a truck to go with it.

https://www.fleet.ford.com/showroom/...r_F250_350.pdf

 

I have an 03 crew cab , 5.4 with 4.30 and pull a 10,000 pound fifth wheel and it does just fine. I saw a slight bump in fuel mileage when changing gears. Now if I was a fulltime RVer and doing lots of towing around the country then a diesel would be the ticket but for us weekend warriors the 5.4 does the job and doesnt complain like alot of the diesels do.

 

My truck is a cc long bed 4x4 with next to no options. The truck with a full tank of gas with me in it is just under 7000 lbs. Simple math tells me ill go over the gcwr with just about anything bigger. Anyway I've been looking at the light and ultra light 5ths but even then they can run 8k to 10k lbs. Ill be looking into 4.30's more and even 4.56s.

Thanks for the Info fellas.