I have a 2000 4.4 Sp which was purchased in June of last year. I had the dealer install the Dinan chips for transmission and motor last fall. The vehicle now has 30,000 miles and about half of these miles have been with the performance chips. Immediately after installation I felt the vehicle was quicker but I was not pleased with the sometimes hard shifting of the transmission. Now after some time has passed either the shifting has smoothed out or I have become accustomed to it. On a trip to Mexico over Christmas we had the speed up to 138 and it could have gone faster. How much faster I don't know because when I realized how fast we were going I slowed down. Gad mileage is about 18-19 on the highway.