Intermittent power loss 2000 305 CID 220hp

I have a 2000 mercrusier 305 CID 220 hp Alpha engine (fuel injected) in a 2000 Maxum 2400 scr. Bought 1 year ago at 100 ft sea level. Ran like a champ at this elevation. Boat now used at 6200 ft elevation. Has less power because of elevation as expected, but at times boggs down and will not go over 10 mph. Later will run fine. Maybe same day or another day will go back to bogging. Of course when Boggs can't get even close to plane. Had tune up, not much done, changed plugs, had mechanic check out fuel flow, no help. Anyone have any ideas?

Start with basics... When it bogs, pull the primary fuel filter and carefully (i.e. while hanging over the side, don't want fuel fumes in bilge) pour contents into a glass jar. Check to see if water seperates out over 10 to 15 mins. Run bilge blower for 10 mins before attempting a restart. If mechanic checked out fuel flow while engine was running OK ( doesn't it always when you get it to a mechanic???) and it was OK, nothing was proved or disproved.

When I pull my fuel filter seperator to check for water, I always smear a thin film of engine oil on the rubber gasket on the filter b4 reinstalling. In these days of ethanol laced fuel, investment in a filter wrench is money well spent. I've found that the type that fits on a 3/8 rachet drive and fits the top of the filter as a cap to be better than the band type... They are available at most good auto parts stores. Make sure you get the right size for your filter. I don't have a lot of clearance under my filter, so I have to remove the wrench ( I have to pop the 3/8 drive off the cap wrench first) as soon as filter comes loose a full turn.

I had the mechanic check fuel for water when I had the "tune up" done. No water was the result. Sometimes I can start the boat and run for hours with no problem. Sometimes I will run the boat for a period of time, then shut off for a swim or some other reason, then restart ( no problems starting or restarting ever) then when push throttle full on to get the boat to plane, it will not get up over 10 mph. I used the term "bogg" before, but it isn't sputtering or dying. The engine sounds like it is running ok just very little forward motion. No telling when this is going to happen.