Not sure what you mean by true mileage. I have the workhorse 8.1 and upgraded the ECM with the unit from UltraRV and what a difference. Plus the service is awesome from them as well. I had to end up replacing a defective Mass Air Flow sensor that was detected in the before and after scans. Not sure I got better mileage, but I did not buy my RV to worry about mileage. It is what it is.