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Discussion Starter #1
New to the diesel world and this forum.

I have an '09 FX4 with
* Fab-Tech 6" basic system lift
* Bilstein 5160 on all four corners
* Dick Cepeck 37X12.5X20 Fun Counrty
* H&S Minni Maxx
* Gearhead 6.4 Tune by Matt
* S&B Si stage 2
* 5" Flow-Pro
* 3" Pipe from Intercooler
HP should be about 550 @ the rear wheels and about 1050 ft lb of torque.

I ordered the truck with 3.55 gears when I bought it new along with the 18" wheels.
I have just put on the 37's and Matt re-did my tune for the new tire size.
5TH gear TC will activate at 60 MPH.
@ 65 MPH, RPM's are just over 1500.

With all that said, my hand calculated mileage is 15.5. I thought I would get
a little better fuel mileage. 15.5 is what I was getting with my previous tires which were 35X12.5X20 MT ATZ's.
Before making the leap to a higher gear, I wanted ask for some knowledgeable opinions.
Do I need more HP/Trq to turn the 37's with 3.55's or is 4.10's the way to go.
I'm planning on going with a Jr. High-Power Compounds set turbos from Elite Diesel which is said to make about 700 RW HP with stock injectors and upwards of 800 RW HP with larger nozzles.
Although the 37' look real good with the 6" lift, I may go back down to 35's depending on the research.
What do you think.

177 Posts
Add more power & you add more stress to the drivetrain. Especially if you put a load behind the truck. Spend the money to regear.

I had a 02' F150 (bought it new) with 39.5" iroks geared with 5.13 gears and 190k on the clicker and towed with it reguraly. Truck still has the stock tranny and my best friends daddy bought it, its his DD now.
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