Hello and thanks for donating
This actually has nothing to do with the vehicle's computer or electronics. It is actually more of a science thing. When the vehicle is in higher altitude, such as when you were on your trip, there is less dense air and a reduction of the engine power. The engine having less strain means the MPG will go up. Going to lower altitudes means the air is a bit thicker which in turn puts more strain on the motor and once again lowers your MPG.
Thursday, July 15th, 2010 AT 10:26 PM