Hardy,
I can't quote any specifics on the performance differences, but if I recall, the exhaust system is attributed with approximately 10-15 additional horsepower on an average V-8.
I know that don't sound like much, but I can tell you the truck had improved acceleration and seemed to breath a whole lot better.
Since then, I've also added a K&N filter, and a PowerChips performance chip.
I pull a 27 foot 5th-wheel, and a 18.5 foot inboard boat, about 72 foot long and 12 or 13K lbs, at 5,000+ ft. elevation and can cruise 70+ mph all day long.
