MTU Series 60 Won't Rev Over 1500 RPM

First, thank you all for the advice, made it much easier for me as a first time sportfish and diesel owner. Definitely an educational experience for me.

Both engines had leaks at the intake manifold gasket and were done. The tech’s computer was not very helpful. He found the leaks by putting in earplugs and his earmuffs then feeling around the engines as I ran the boat as high as it would go.

I would not have known where or what to feel for nor have been brave enough to crawl outside the engine while someone I did not really know ran the boat. Definitely earned his wages.

He also found some impeller pieces at the heat exchanger intake in one engine and an anode from the fall service that had come loose again in the heat exchanger intake of the other engine. I will be doing anodes myself this fall.

How often do you guys change the impellers?