gonna really kill the gas mileage in an 04 F350 w/ 5.4L and 3.73 gears?

 

Yep, the 5.4L will see an average of 12-13mpg stock in such a heavy truck. The regular cabs are ok, but the extended and crew cabs take a larger hit in mileage and power with that engine. Expect about 10-12mpg with the 305s. Thats alot of extra rolling resistance to get moving as well as having an overall taller gear ratio when you're done isn't helping either. If you had 4.10s, 6spd, and a regular cab you might do ok.

 

Put a chip in the truck and you will improve the mileage 3 to 4 miles better.we have 456 gears and 40 inch tires in our power stroke and get 14 to 16 in the city with the chip and 4 inch exhaust.

 

That may be true (although rare) on a PSD truck, but gas engines are completely different when it comes to tuners. Diesels can get true 100hp gains from them as well as pick up mileage. 3-4mpg more is very rare, and if you're going off the overhead console it won't be remotely close to right. Most people see 1-2mpg more MAYBE. Mine didn't change at all which is very common. The gas trucks MIGHT see the 1-2mpg gain, but for the most part they won't see much of anything. Most gassers may get 15-20hp more from tuners at most, and thats usually running on premium gas. Theres really not alot out there for a gas engine thats going to boost the mileage back up to make up for larger tires. Even if you do get the mileage back up it will cost you more than you'll ever make back in fuel savings. Sorry, but welcome to the world of a 1/2 ton V8 gas engine put in a 4 ton truck.