Whenever the exhaust regen occurs on my 2012 3500HD Duramax, I have noticed 2 things. One, idle speed increases about 200 RPM; and two, fuel mileage steadilly decreases for the 20 minutes or so regen occurs. Running empty, fuel mileage will ultimately be reduced 2 to 3 mpg. Will regain perhaps 1 mpg (at best) of that loss before next fillup. Is there any way to reduce that mileage impact?