Gear Reduction help

I have a 1991 V6 4x4 with BFG 31''. I only get 14 MPG. I read an article saying that my problem could be a gear mismatch because of the tires, it says that I need to make a gear reduction to 3.8 to gain some efficency. How do I do this? I did some research and I think that the stock ratio is 2.66 and also that I have to change the ring and pinion to get the desired reduction. Am I right? also, do I have to change anything on the front?? Please help me, and thanks in advance.

Your completely right. Your going to have to change out your fianl gears/differencial gears/Axle gears(what ever you want to call them) to achieve this.

This is not the easiest project to accomplish, but there is more then enough information out there for you.