EBung said:If you have a 2000 and up Auto truck it makes a big difference on launch and 2nd and 3rd gear shifts. Plus if your really crazy the top speed eliminator feature is nice too! I like mine but I only use it to embarrass someone REAL bad at a stoplight. When the switch is on the tach doesnt work and it sets a check engine light. The light will go off a couple starts later. I believe the top speed eliminator feature works whether the switch is on or off.