It is hard to say, if it is spark or fuel. From what you say about the gauges, it appears that power is getting to the key switch and the key switch is at least keeping power to the gauges.
I do not know about the vapor lock theory...but
Since you have already checked most of the electric stuff (if you did what I suggested in the last post)...I would turn to the fuel. If you can cruise at a lower rpm with no trouble, but the trouble only happens at higher rpm, then the motor may just need more fuel. Either there is not enough fuel getting to the vapor separator or the vapor separator/high pressure pump is not providing enough fuel pressure.
It could be clogged fuel injectors, but if you can run at high rpm for at least a little while, then problem injectors are not very probable.
What did the fuel look like when you drained the vapor separator?
Did you happen to have someone squeeze the fuel bulb when the motor was failing? If not, give it a try. If it takes several squeezed to get hard and the motor starts performing better, then it is definitely fuel...but could be any number of things.
Have you ever changed your high pressure fuel filter? It is inside the right end of your vapor separator.
Have you changed you low pressure filter?
If you have just changed your water separating fuel, make sure that the two plugs in the filter are sealed properly and are tight.
Make sure all of your fuel lines are connected tightly...do not rotate on the connector...etc.
Make sure your fuel bulb is good and gets hard when priming engine. It should normally lay either horizontally or ideally with the arrow pointing up. Depending on your tank, it is possible that you could have lost fuel out of the system back to the tank through the fuel bulb (while you were sitting in the cove), if one check valve is bad and you do not have an antisyphon valve in the fuel tank.
It is possible you are sucking air; the low pressure fuel pump is getting weak or failing; the high pressure filter or lower pressure filter is somewhat plugged up with debris; the fuel bulb is bad or in incorrect angle (could be blocking fuel passage), tank vent might be clogged, etc...
If you can borrow a new fuel line and portable tank from someone, that will eliminate an issue with the tank, water separator, hose, etc.
Another angle...if no answers are appearing with looking at fuel....take a timing light out with you and if you can make it fail...attach the timing light to each spark plug wire and watch what happens to the flashing when the engine fails. Try this on each spark plug. It is possible you are just loosing spark in two cylinders. Until you do these checks, you really do not know which way to look.
Sorry for the rambling...there are a lot of things to check.
Mike
