3.92 gear

How realistic / costly is it to switch a truck that comes with the 3.92 gear ratio back to a 3.21? I’ve found several trucks that I like that have the 3.92 instead of 3.21, but I do not need the 3.92 as I do not do a lot of towing. I realize this may be a really stupid question.

Off Road Skid Plates w/full size 20in Faulken Spare Tire. Also, a shot of the rear suspension spring.