It is a 2003 F-150 Supercrew 2WD 4.6L w/3.55's w/stock 17's

I want to move up to 4.10's but want to make sure I buy the right gears. Is it a 8.8 or 9.75 ?? and do you think 4.10's is enough for me?

I am just tired of the truck downshifting for every little hill. I think if it didn't downshift all the time, I would get better gas mileage. The main reason I want the gears is a little better get up and go, not gas mileage as I know gears will hurt me in gas.

I am also planning on different tires later . 20's or 22's ..

 

It is probably the 8.8, but to be sure look at the tag on the diff. It will usually have something like 88 or 975 on it along with the axle ratio.