[b454rat]

Take your 38s and divide that by the stock size tires, say a 31. Mulitply that by the current gears, we'll say 3.42s, which comes up to 4.24, so you can go down to 4.10s, or up to 4.56s. Depending on what axles you have, going to a 5.13s will make the pinion real small, and with 38s and a healthy motor could make them and the joints go pop.