I also have a 2000 GS400 with the Swift Racing Intake and ECU. I have a TC coming in hopefully today. It is a Lextreme! THe Dragon is by far the best, but also very expenssive! The Lextreme is resonable priced and will ad just as much performance. One of my co-workers has a 2001 Lexus GS430 with a Dragon TC that he installed last week. It made a very noticable difference in off the line power! It is the best bang for the buck if you want more power! Good Luck! I will let you know what the Lextreme feels like once it is on!
