For 37" tires, you'd probably want to go with at least 4.56s. You could go with 4.88s to get better acceleration, but your RPMs at highway cruising would probably be pretty high and cost you even more fuel economy that you're already going to be hurting on due to the tires. For a complete gear package for your truck, give us a call directly at 623-434-5277 or email us at [email protected]