Gear swap in a 00 F350 Dually

[boostforfun]

Hey Guys,
My dad just bought a 00 F350 7.3 6sp 4x4 dually truck to haul freight with. I think he will be pulling the 37' gooseneck flatbed that weights about 6500-7k dry. On that, we will be loading anything from 1k-13k worth of freight. The truck currently has 63,000 miles and bone stock.

We are ordering a PHP Phoenix 6 position with stock, 25 heavy tow, 40 tow, 65 tow, 80 daily driver, and high idle settings. Truck will have boost and pyro on it when chip goes on.

My question is this: The truck currently has 4:10 gears in it, and we are concerned about fuel mileage (as all LTL hot shotters are). I was thinking about swapping 3:73's in, and was looking from advice from guys that were running both gears.

Also, has anyone out there done this swap? I have a buddy that has set up a few in mustangs, camaro's, and his own 67 chevelle. He has all the proper gauges to measure backlash, and none of his cars have ever whined when set up. Are the Super Duties anything magical to install? Does the 4x4 equipment get in the way (ie, do you have to pull the hubs and junk to pull the axles to remove the R&P, or can you just slide them out enough without removal.)

Any other fuel mileage tips beyond the better exhaust, better intake, chip discussion would be greatly appreciated. I have only owned cummins till now, and am new to powerstrokes.

Thanks in advance!!

[panheadjay]

yes the axels have to be removed, if i remember right 4.10 ring carriers are different than 3.73. that could be pricy. mybe a tech will chime in and confirm me wrong.

[Dietoremain]

I'd keep the 4.10's for the pullllllllling power but thats just IMO.

[NCHornet]

For your plans with the truck I too would keep the 4:10's. BTW you found a real gem there with only 63K on it, good deal!! I have a 4:10 2000 dually and I will tell you that rpm's makes a huge difference. I can get 12 mpg towing my 9500lb+ TT, if I keep rpm's below 2000. But at 2000 I am only going 60mph, kicking it up to 65 and I go down to 10mpg and 70mph gets me 9 or less. Tire pressure is also important to keep an eye on. Before installing the chip you need a better flowing intake to keep EGT's down. You also need a better flowing exhaust, not a new system, just remove the factory muffler. Ford saved hundreds of thousands of dollars by using a universal muffler on the SD trucks, they necked down 3.5" plumbing to 2.5" to go through a offset muffler that caused more restriction. Backpressure is good on a gasser but not on a diesel. Get a Walker BTM or straight pipe it and you will be good to go.

[boostforfun]

At best I will be able to put a BTM on it. My Dad is kinda a nutball when it comes to keeping things relatively stock, and he doesn't want it very loud for pulling all the time. I have a buddy with a straight pipe 7.3, and that is way too loud for him under a load.

I knew that the 4:10's would be a little worse for mileage, but better for pulling. I am hoping that be keeping it under or around 2k on the 80hp DD setting, he could get decent mileage (empty, of course).

I'm just trying to get the truck on par with my 07 cummins for pulling, as my dad likes driving that truck, so the closer I can get to 325hp and 600 lbft, the better.

I appreciate all the feedback.

[panheadjay]

your milage would probably drop pulling with 3.73's. mine has 4.10's its not that bad, just don't drive it hard. mine gets about 16 empty or a light load, at 64mph, 12-13 at 74mph. whats that cummins get pullin a heavy load?