Well, got my LX410 back from the dealer today. They determined it was a fuel starvation issue. I walked in their shop yesterday about the time they had figured this out. Shop guy and Yanmar rep said they observed air bubbles in the fuel strainer ( the clear plastic bowl under the right fender, visible from the rear of the tractor ), and actually saw the bowl try to cave inward as the little booster pump that transfers the fuel forward attempted to empty the bowl.
The shop guy pulled the fuel line off the tank fitting, and only a little fuel dribbled out. He stuck a thin screwdriver up in the fitting, and fuel gushed out.
So they removed the tank, and sloshed a little fuel around in it, and poured it out using a shop rag as a filter, and found some plastic shavings that they suspect was left in the tank when the holes were drilled for the supply and return line fittings that go in the bottom of the plastic tank. The fuel line is really small.....looked like about 1/4" to me, maybe 5/16" tops, so it wouldn't take much to block it.
WHY they don't have a bigger line, at least to that fuel strainer, as well as some kind of screen that sticks up an inch INSIDE the tank for a fuel pickup is beyond me. But if it ever happens again that something gets in my tank and blocks fuel flow, I'm going to Tractor Supply and buy what I need from the sprayer section and "field modify" my tank to prevent that stupidity.
SO FAR, the tractor seems fine. I remain cautiously optimistic.