I have the 5.4L and going to regear next month but i have a question before i do it.......

Going with 4.56 gears from 3.55's will lower my mpg's wont they?????

running at a higher rpm = more gas burned?

 

Stock tire size? If yes the it will decrease the mpg. I think with 35s you'll see an increase of mpg.

 

i have 35's (35x12.5R20)

 

Running at ahigher rpm doesn't always mean you burn more gas. Think about the other aspects involved too. With the increased tire size, you will have effectively lowered your rpm's at speed as compared to stock. If you go with the right gear size, all you will be doing is returning that ratio back to the way it was when you bought the truck. Also, it takes a lot of work from your engine and tranny to turn those 35's w/ the OEM 3.55's. A lot of work because of the increased size and weight. More work= more gas. By putting lower gears in(higher in number), you ease the strain on those 2 major components and by doing so decrease the amount of gas used not to mention wear and tear. On the flip side, if you lower the gear size too much, you WILL effectively increase the ratio over stock and burn more gas at higher rpm's. It will increase your performance and pulling power though.

I have 4.88's in my truck and get worse gas mileage now that I have an under 100lbs., 33.4" wheel/tire combo than I had when I had the same gears with a 140lbs., 37.75" wheel/tire combo. I average 1+mpg less now though I do have significantly increased performance and ease of acceleration.

 

So by going with a 4.10 - 4.56 gear i will be getting as close to stock as i can and will in turn(by keeping my foot out of her) get better gas mileage???

 

that is correct