[scotte]

I have the above mentioned set up in my truck. 99 F-350 4x4 CCLB SRW 4" exhaust, AFE big boost air filter with 3.73 gears in the rear running 285/75/16 tires. I just took a 500 mile road trip in my truck with 450 being interstate. On the interstate I ran at 2000 RPM's but was only able to get 15 MPG that is what I was getting pryor to installing the tunes. I'm very happy with the performance but not getting addation MPG. I was hoping to get 17 to 18 MPG after the upgrades. Any ideas or is this what I'm goint to have to live with? I also have a 65hp tow tune and 120 performance tune that I have not used yet. Thanks Scott

[cleatus12r]

All trucks are going to respond differently to tuning, and I would certainly give the tuning a little bit more time as you said, "I'm very happy with the performance". Additional power means additional fuel....no way around that.

There are a lot of things that affect mileage. Since you have 285/75-16, I assume that they are 8 ply tires (very few manufacturers of 10 ply 285s). These only allow you to run 65 PSI at a maximum. Any sidewall flex causes rolling resistance, so make sure you are at the maximum inflation pressure if you're trying for improved mileage. Alignment also plays a role (especially toe) so if you're experiencing any kind of weird front tire wear, an alignment may be in order......and don't just let the alignment shop get it "in specs"; be sure it's exact. I did it for years......it's not that difficult for them to do the job they get paid to do.

Certain trucks just don't get good mileage. My brother's 99.5 is a great example. Same truck as my previous 2001 but with a set of larger tires. He's stuck at 14-15 on a good day while my old truck with the exact same tuning was getting 18-19.

Remember, with a diesel, it takes a certain amount of fuel to make a certain amount of power at a certain RPM. Tuning changes can make the engine slightly more efficient, but if the truck takes 50 HP to maintain 65 MPH on level ground with stock programming.....it's still going to take 50 HP after the tuning is installed.

[scotte]

Thanks Cody I will begin checking what you have mentioned.