oil pressure does not go down when the engine speeds up. you have a problem with INDICATED pressure, not actual oil pressure.
the best thing you could do is remove the oil pressure gauge and throw it away. if your engine needed one, Harley would have installed one before they sold it. that's up to you. if the low oil pressure warning light is on, you do not have low oil pressure.
the factory spec on oil pressure for your engine is 25-35 psi at normal operating temperature and highway speeds.
that said, you most likely have an issue with the engine breather.
there is a hose on the back of the engine, just inboard of the oil pump that connects to the back side of the air filter.
-ensure it's not kinked or restricted in any way.
- make sure the oil tank level is between 1/2 and 3/4 full with the oil at operating temperature (typically checked after a ride of 30 miles or more)
- never change the oil or top off the oil tank without first starting the engine. again, the best time to do this is after a ride.
check all those things and let me know what you find.