I currently have 3.55:1 gears in my '04 f-150 Screw, was wandering if the switch to 4.10:1 gears would hurt MPG as much as people say?

Also, were can I get those gears. I'm a novice on this subject.
as always thanks!

edit; P.S. tires are stock 29.5 inch

 

most people base the change with larger tries and gears its not really gonna be much worse maybe 2-3mpg at most now thats if you granny drive it more if you hard on it like most of us