I have the Dynomax 19430 on my truck. Installed it a month or so ago. The Y-pipe isn't much bigger than stock, the passenger side pipe is still a pretty drastic T shape, but the bends are miles ahead of stock. I can't attest to mileage gains, because I only had the truck about a week before I did it. But the power is far better. I'm in Central Indiana and I'm pretty sure I still have the stock Y pipe, if you need it.