I've got the round speedo gage (GPS) and all of sudden it started fluctuating between 67-72 when actually running 74 (per the 332c). I thought it was a fluke but on the next trip out it only goes up to 64 max and then just stops reading any accelerating from there. It continues to display 64 regardless of actual speed (above 64). It works fine and is in sinc with the 332c below 64. Any suggestions?