Why might my throttle handle on my starboard engine not go as far up (increase rpms) as my portside. Used to until yesterday. This causeing my rpms to be behind the portside engine. Something out of adjustment?

This exact same thing happened to me a couple weeks ago. It turned out to be the tach for that motor was going bad. It was reading higher than the other one, so when you compensated to get the two tachs the same...one stick was farther ahead of the other. Take your gauge panel out...switch the sender wires (easy to do) then see if the opposite happens with the throttles. Mine was doing it intermittently. Bought two new Gaffrig tachs....problem solved.