motor adjustment for altitude

[BURLEY]

I'm running a 2015 60hp mercury 4 stroke EFI on a 16 ft Tracker weighing about 1300 lb.. I have operated it in Ark. at 900 ft. elevation, C.J. Strike, and recently at Strawberry. It seems to do better at the lower altitudes. With only 1 larger passenger at Strawberry I had difficulty getting on plane. It has a 12x22 prop.. Is there a simple way to get better performance at the higher altitudes? The boat was purchased at Fred's so I would think that it would be propped for our altitude.
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