None at all, it makes it feel sharper, 2,3,4 have more pull, can't say I notice any MPG gain as I've had it on so long. Have taken it off for servicing and if the car went back (paint work issues). easy to connect and run.
If you do get it when you first install the engine managment light stays on, just switch off and then on again and its gone that only happens when the map is put on either first time or after a re install. Found superchips very helpful if needed.
I still average 53mpg but still not done a long run.
Any other concerns let me know
FLC