Regearing a truck means changing the gears in the truck's transmission to make it more efficient. This can be done for a number of reasons, but most commonly it is done to improve the truck's towing or hauling capabilities. Regearing can also be done to improve fuel economy or to simply change the way the truck drives. No matter what the reason, regearing a truck is a relatively simple process that can be done by most anyone with a basic understanding of automotive mechanics.