The GPA is driven into the water at a slow pace in low range First gear with the prop PTO engaged and spinning. Once in the water, the wheels are disengaged by placing the transfer case in Neutral. The highest speed, 5.5 mph, can be obtained by using Second gear and full throttle but it only delivers about 1.25 mpg. Third gear full throttle delivers an extra mile per gallon but 1 mph less speed. The most economical combination is Third gear and quarter throttle, which delivers 5.5 mpg and 2.5 mph. High engine speed and load can result in overheating.