I am contemplating an engine swap in my pickup. I drive a 2003 Chevy silverado 1500 Z71 with a 4.8L. I have put a 6" lift with 35s on it and the 4.8 just doesn't have enough power to push th struck now, not to mention the horrible gas mileage. I bought a diablo sport tuner for it but for some reason it doesn't help enough. I need more power. So I need to know which would be the best route, a 5.3L or a 6.0L. I want it to be either one of this so that my tuner will still work. Will I need to change transmission along with motor? I need some help and I don't want to be swindled by a mechanic before I have the right info. If an engine swap is too costly, what are some cheap and easy ways to enhance my performance and torque.