Is that what I should expect from a tune? :shrug01:
I have a '06 M6 Vert. The only thing non-stock are the NPP mufflers.
The tune would give me more than 400HP and better fuel mileage?
Yes, it should Lou. The engine should be more efficient which in turn provides more power and better fuel mileage. Of course there are no guarantees but that's the norm.
Timing, fuel trims, shift points. In your case forget the shift points. These are just a few that are normally easy to tweak and will make a difference. I would start with a scan to see what's going on and then tune from that.