Yes, on a 4x4 you have to do both axles which doubles the cost. It's not a DIY project either. Take it to a good gear shop and have it done. Runs around $750-$1000 PER axle.

But the point is, it is the only thing that will make a dramatic difference in towing power. Exhaust, intake, tuning, will only make small improvements in HP and when towing you won't feel a thing in the seat of your pants except for a thinner wallet. You will FEEL a gear change.

Bill