I’m the original owner of this motor which sits on a 20’ Bennington, since day one this engine has always struggled to run smooth at 2000 RPM. At 3000 she purrs like a kitten. Lately while at 2000 rpm, it will fall off 200 or 300 RPM and then jump back to 2000. It seems like every 45 seconds give or take. I’ve run SeaFoam, replaced plugs, and still same problem. Any suggestions??