I'm restoring my 1998 Z71 5.7 5-speed extended cab truck. I switched to 235/85/16 tires and I'm getting ready to replace the exhaust system. In doing this, I'm also in the search to the highest fuel mileage possible as a personal project. I've decided to go with a Flowmaster cat back system, but I'm looking for input on single or dual exhaust? Also, which brand of shorty headers would work best. Of course I want it to sound good, not terribly concerned about a power increase, but looking to increase mileage for shirt trips out of town. And has anyone done any computer/chip upgrades that effect mileage? Any input would be appreciated.