1994 Carver 390 CPMY with mercruiser 7.4L carb engine. The carb was rebuilt by the marina this past winter. When I brought it home, it would get up to around 3800 and that was it. I also noticed a slight vibration/shudder akin to a misfire. I did a shake down run today. Seems OK up to 3200 then the engine sync gauge was a little sporadic. With that shudder, that was on the port side. I dropped anchor and changed the gas filter. No improvement. Now it is smooth as heck up to 2000. However, once above that it has no power sync guage jumps and shakes. Engine got new plugs, cap, rotor and module last fall. Seemed to run great. However, not so this spring. I checked cap and rotor and looks great, no pitting or flashing. I am lost. The only change was the carb rebuild by marina. Engine has 1100 hours and has even and strong compression per the marina last fall.

Any ideas? I am lost.