I have a 2003 f-150 fx4 with a 4.6 and 5spd. I added a flowmaster and k&n, and also put on a set of 305/70/17's. Since these modifications i have lost a lot of gas mileage. Any help to regain some mileage would greatly be appreciated.

 

Original tires - 265/70-17 - 31.61"
New tires - 305/70-17 - 33.81"

Your new tires are 2.2" taller than the speedometer is programmed for. This means you're traveling quite a bit further than the odometer is recording. Unless you have the speedo recalibrated, you're not going to know how far you've actually traveled just by looking at the odometer.

I'm not sure if the dealer can program the new tire size into the computer or not. 305/70-17 is not a stock tire size.

 

Your gas mileage may have gone down but,
haven't you noticed that everything is so much closer now?

 

If the dealer can't reprogram my speedo, I guess the only alternative would be to buy a programmer. If so, which one would you recommend?

 

See if anyone else chimes in here. I'm not familiar with the M5OD transmission. There may or may not be a gear you can change. I'm not sure.

You could call or e-maik Mike Troyer at Troyer Performance. He could tell you if the Micro Tuner will work and he's also a supporting vendor here.