Bought a 2002 2 months ago, motor shit the bed @ 129K with a oil pump failure. Got it swapped under warrranty for a 2004 5.3L with 110K but I can't really confirm if the ECM was swapped. My question is, what improvements can be made for power & efficiency that are CONFIRMED. I know everyone sells products to give you all kinds of claims, but I am looking for people whom are users that have hand calculated real numbers. Here's the truck , stupid clean, I couldn't pass it up for $5K , wife's Chicago area winter vehicle.