We are cruising on our Catalina, 36 mark two along the south coast of Lake Erie. On our way to the thousand islands. Yesterday a mechanic did a little work on the boat at a Marina and told me to run my engine up to 3500 to blow out the carbon more frequently. In gear, I can only get 2500 out of my engine, perhaps the tack is not reading properly. 
today when we left the marina, I could only get 1900 RPMs out of the engine, even though that setting took me well up to hull speed, and a bit beyond. It just does not sound normal at the higher rpm. Both fuel filters have been replaced, and before we left, we basically serviced the entire engine system. this included the rebuild of the water muffler system. Any thoughts on what has gone on?
two days ago, we had a log, and I thought perhaps we damaged the prop, the engine also seems to have more vibration. Any help would be greatly appreciated t, thank you, Rich.