RPM gauge (Not smartcraft) is maxing out periodically (once per day) last 2 trips to the lake. No warning horn, rev limiter horn, etc. ( 2011 Mercury Optimax 200XS). Ran 20 miles one way Saturday a.m. at 5800 RPM 70 MPH. Moved several times without issue. Later in a,m. RPMs maxed out during short run. Cut off and fished. Cranked her back up and remainder of day had no issue, including return 20 mile run. Is there something wrong with the gauge, because there has been no difference in the performance of the motor?