What would be the best gear ratio for my 98 f150 5.4 4x4?
What is the stock ratio?

 

3.73 if I remember right

It should say it on the sticker in you door frame, and stamped on the rear end housing

As far as about what you SHOULD run...I have no clue. There's guys that swap up to all kinds of gears depending on what size tires you want to run. I've seen as high as 5.56's for 35's. But tons of people running that same size on whatever the stock gear size is

 

Most likely you have 3.55s. If you have upped the tire size and/or want more pulling power a regear to 3.73-4.10 would really wake your truck up!
In an attempt to get best in class fuel economy numbers, ford geared these trucks a little to high(numerically low numbers) in my opinion.

 

my truck got better mpg with a lower gear. Currenlty running 3.73's on on 33's and feals similar to stock with 3.55's and 31's. But when time comes for a bigger tire and lift I'll be running 4.56 instead of 4.10's.

 

We need to know what tire size you plan on running as well as if you do mostly highway or city driving. Also, what are you trying to achieve? Better mileage? Harder pull off the line?

There is more than 1 ratio that came in the trucks.

 

I don't use this truck much burning just want harder pull more power