I have installed a borla exhaust and a set of short tubes on my wifes 04 5.3 yukon 4x4. I have modded the air box to get the K@N flowing better also. After the headers I noticed a huge drop in torque. Upper RPM power is amazing though. NAy suggestions short of a cam install. The wife is not big on seeing the grocery getter torn downm in the garage. Also has anyone tried a 160 thermostat to keep the clutch fan from robbing to much power? Let me know what you all think.