Good Morning!

Has anyone experienced problems with the gambler fuel fill vent? My 2002 2100 Merc 250XB runs great up to "full speed" but on long runs it will shut down to an idle (but doesn't die). After 3-5 seconds I can apply throttle and it will run with no issue. I haven't experienced any performance issues at mid RPM range 4500-5500. The dealer recently serviced entire fuel system from tank back, new lines, clean flow injector, all new lines under cowl, VST clean, rebuilt pulse fuel pump, new filter, etc. So I don't think this is engine related. I'm thinking vent or fuel pickup restricting fuel flow?...and the issue was there prior to this work....was hoping replacing the old lines would fix it. Engine received a clean bill of health with regard to compression and leak down so it is healthy.

Please advise if you have any thoughts on how to check or what to check?

Thanks..Justin