Well, I got mine in yesterday and installed it today. The installation was a bit more of a PITA than I expected, mostly thanks to the fuel lines not being long enough when the spacer is installed. I noticed an immediate increase in power both on the bottom and top end. My Suburban now chirps it's rear tires with no problems, something it could not do at Denver's altitude before. The top end has more get up and go as well. I'll see what kind of mileage improvements I get, if any. I'm making a trip to Amarillo, TX this weekend. Last time I went, I averaged 12.xx mpg.