01 and 02 are basically the same both have LB7's in them, the 03 has the new body style with LB7's as well. In 04 they changed to the LLY. The LLY was improved torque & HP:thumbsup: , but lost fuel milage:eek: . IMO I would go with an 03, if you add a chip, exhaust, and intake you will get...