Check the tachometer as well. The tach on my boat is shot and reports 2000 rpm when the engine is actually turning 2800 rpm. I tested it using a digital tach measuring a point on the flywheel.
I've adapted, but I should also replace the tach someday.
I have checked the rpm's with a digital tach, it it appears fine. However, I do have a problem when my batteries are full, the alternator doesn't put out so my tack reading is off until I turn on a blower or something.
I guess a side question would be, anyone know how to get the tach reading from the engine and not the alternator?