assuming you have 3.73s, your truck would take about 5 minutes to get to 60mph and your tranny wouldn't last very long.sandaddiction said:Im going to be doing a 12-15inch lift on a 04 ext cab silverado 4x4 with the 5.3. I am going to be most likely running 20s and 40s. Do i need to regear? What will happen if i dont?