I don't think that going up just one size will make a noticeable difference. In my opinion, it is not even worth the expense. It cost exactly the same in parts & labor to go up to 4.10 or even 4.56.

 

You could get gears from JEGS for as low as $149.99.


JEGS #555-60027

Ford 8.8" Ring & Pinion
4.10 Ratio
41-10 Teeth
More Details $149.99
JEGS gear sets are made with high-quality grade steel to provide long-lasting use for street, highway, and the occasional race assault. They're manufactured utilizing modern machining and heat treating for added strength and durability for miles of trouble-free service. Marking compound and sealant included

 

My truck has Ford Racing Performance Parts. FRPP offers gears in 3.73, 4.10, 4.30, & 4.56.

Richmond Gear is also a recommended item.

A programmer will help with programming your truck's Powertrain Control Module. Unless you reprogram with trucks computer with the proper gear ratio, your speedometer and odometer will be off. Your truck's computer will still read that your tire has turned 1 revolution with every 3.10 revolutions of your driveshaft; when in fact, your tire has net yet completed 1 revolution. Your truck's speedometer will show that you are driving faster, and you odometer will show more miles.

 

You will need:
Ford 8.8" Ring & Pinion w/Install Kit
4.10 Ratio
41-10 Teeth
555-60027K

Ring & Pinion Set Up Tool Kit
555-81655


This is also nice to have:
Rear Axle CoverFord 8.8'' 1981-Up
555-62500


This is even better:
Mag-Hytec Ford #10-8.8


Do it like this:

 

yeah, a TBS is designed for carb'd engines. Like sgs said, it's IMPOSSIBLE for you to gain HP with a TBS on a FI engine. It's like trying to turbocharge a turboprop airplane. There is no need for it and it does nothing but add weight and a annoying little whistle at highway speeds.

However, if you are looking to do some SERIOUS mods, get the Tornado fuel saver system.

 

And stickers.

 

Buy a bigger truck? I mean come on its a 6 cyc.