I had something similar going on with my motor this spring. (running at WOT the motor would cut out intermittently and then run OK) Cliff took a video and we sent it to Bernie and his first thoughts were a possible coil going. (Actually started my last trip last fall and thought it might be plugs. Put new ones in this spring and the problem was still there.)
I was fortunate enough to be going to Bernie's soon after this and he brought out his timing strobe and we went for a ride. After checking all the wires/coils the problem was on all of them. He started moving the wires on the motor around and found pushing them one way and all was good but when pulling them the opposite the motor would act up. Went back to the dock and he found a terminal had broke with 3 wires going into it. He saved as much of the wire as he could and put on a new terminal, bolted it back onto the motor and that was all it was. Been out a few times since and the motor has run perfectly. Could be as simple as a bad wire somewhere, maybe a coil.
Take some video your next time out and show that to your repair guy if it is still acting up. If you have someone with you on the next trip, take the cowling off and go for a ride and do the wire wiggle test and see if that gives you some answers. Better yet, check all your wiring before you head out. My broken connection was a bit hidden.