Ive been trying to get to the bottom of why my 89 F-150 is such a snail when it comes to pulling a hill. The motor has been canceled out my next thought is that the rear end gear is not low enough for my tire size. I'm running 35/12.50s and i think the truck has the factory gear. Maybe a 4:10 would give it some more grunt?

 

Yes it would. It's a common mod to go with a higher gear when getting larger tires as they do slow ya down a bit.

MPG will take a bit of a hit too but that's also largely depending on your driving style.

 

Gears, definately. I have 31s and 3.08s and mine's a turd too, I can only imagine 35s and probably 3.55s

You'll most likely want at least a 4.10, if not a something lower (higher numerically)

 

There's more than one factory gear ratio. Find out what you have by looking at the differential tag.