The resolution on your GPS unit is terrible.

On rides of 30+ miles, my wife and I have had end results of the exact same distance and elevation multiple times, and the greatest variance has been ~0.25 miles between the two of us. Garmin 500 and 520, respectively.

We don't seem to have a digital doping problem around here. A whole lot of people leaving their app running on the freeway, though. A lot.