4.3L OMC starts, runs a few minutes then stalls - repeatedly?

Hi, I have an 89 OMC. I've had it for 10 yrs or so.

We've had our issues, but generally it has been reliable.

Just got it out of winter storage recently. Went through my de-winterization which includes hooking it up to water muffs. It took a good amt of cranking to start, but eventually did and seemed to run fine.

A few days later off to the lake we went.

It fired immedately on the trailer we took off across the lake. Seemed to be running great, running at 3k rpm or so.

After about 5 minutes it sputtered a couple times, and about 10 sec later it died.

It re-started, but wanted to die as soon as I gave it throttle.

I poked around the engine a little bit, thinking it is a fuel problem, but didn't see any obvious problems.

I pulled off the fuel/water separator and nothing seemed out of line.

I thought there might have been some build up in the bottom of the can, but didn't have a spare so I threaded it back on.

It started, seemed to be running fine. So we took off again.

A few minutes later when through the same process as above.

The 2nd time I pulled the water/fuel separator off I heard a pressure or vacuum release and don't know if there should be pressure (pos or neg) there.

I thought maybe I my fuel tank vent line is clogged (I replaced inlet and ve4nt hoses ~3 yrs ago), but I don't know if it would cause this.

The point is I have no idea what's going on.

Thoughts/suggestions on diagnosis?