Mine gets 18.5-19 pretty regular. I've got 4.10 gears so if I'm on the highway for a long trip doing 70 it'll drop off a bit. I have noticed that the amount of smoke will change with how I drive it. If I've been taking it easy for a few days and then in a hurry one day, it'll smoke for the first few hard pulls and then it won't smoke anymore. When I removed the device in front of the muffler I noticed the smoke went away completely. After a week or so it was back to normal. I still have the stock muffler.

I'm betting the computer adjusts itself to how you drive. That's the way gassers have been for years.