Zero Turn Mower. I'm stumped.

A few years ago I worked in the service department at a green tractor dealer. A customer brought us a good sized but older garden tractor, and complained that it would cut out frequently, and he'd had to push it onto the trailer. It ran fine when it came in. We ran it and mowed with it (a lot of fuel delivery problems only show up under load), couldn't get it to act up. We parked it and had him come and get it. A few days later, I was driving it to his trailer to load it, it died and wouldn't restart. After some more analysis, we fished a red shop rag out of the tank. Somebody must have used it as a fuel cap at some point. We've all seen that. It apparently dislodged itself from the pickup on the trip to our shop, and the harder we worked it the more it floated the rag. It settled back down when we parked it. so you never know what you might find in there! We often removed the fuel tank and flushed it out with a pressure washer. We frequently blew air toward the tank from the fuel pump or carb. That wouldn't really fix it, but gives a place to look if it suddenly runs better afterward.