bigger tires

Do bigger tires mean more speed/acceleration? i know there would be added weight but there would be a greater surface area on the road.

i dont know about that but they will drink more gas then these trucks already do

The only thing a bigger contact patch will give you is better grip. Unless your Explorer is putting out enough power that you regularly spin tires (which I'm doubting it does) than it shouldn't make your ride any quicker.

I have a 98 XLT V8 and replaced my 15" stock wheels/tires with 17x9 Cobra Rs (Mustang type) and 17" Dunlops (65/70-17s) and noticed a remarkable handling difference. Yes, the contact patch is wider. Look for tires that are the same specs but in a larger size. There is a wheel ratio guide somewhere on the internet where you can find similar sizes in tires.