Sorry - I had a couple things on my mind as I was typing a response. Running with the fuel cap off eliminates the fuel vent from the mix... in case it is clogged - which you can still try doing. Either way, it is extremely unlikely that both of the electric shutoffs are partially failing. In case you missed it above, you DO NOT have traditional AS valves. The first thing to do is NOT just start replacing items because some forum, somewhere, suggests it. Rarely do you get lucky and fix the issue on the first try. Check your fuel pressure - that will help narrow things down tremendously. Once you know that, we can go further. You may have the "cool fuel three" issues that has plagued many Mercruiser motors around your model year. FYI... THAT you can go ahead and google - and also search on this forum... lot's of info about that. Or, it could be something else - but fuel pressure is a starting point. When is the last time you changed the fuel/water separators? And what is the condition/quality of your fuel? You can take a sample from the CF3 module. Another often overlooked item is a dirty hull bottom. It doesn't take much to cause the symptoms you are having.