4:10 is all you will need with 33's. I run 33x12.5x15's with a 4:10 and I get right at 24 mpg on the highway. Now, I have a 4.0. My buddies who have the 2500 Mazda or a Ranger with the 4 banger with 33's are running 4:10 as well and they love it. They get good gas mileage as well. You can go 4:88 at the most and that is as much as you should go.
Uhh yeah... I have 4.10s and 225/70s and it blows.
Go with at least 4.88s.