I only ordered a couple things from them, but their stuff was priced well and they shipped really quick. The downpipe I got from them was very high quality. But yeah, you can't go wrong with ZZP either
Thats odd. My GTP had all that plus a 3" downpipe, but I still had the stock pulley, and my mileage didn't change a bit from stock. Although the smaller pulley probably makes a difference.
If you drop down to a 3.4 pulley I'd recommend getting headers. Every car is different though, but make sure you monitor KR. I'd invest in an Aeroforce Interceptor gauge. Best money I ever spent on that car