My Craftman Lt1500, Model 247.288820, 420 Cc Lawn Tractor Stalls Out While Mowin

This started last summer. I changed the fuel filter, gas line, oil filter, etc. The only thing that helped was to top off the tank. That worked the rest of the summer. This year, problem has progressed. You Tube has lots of videos about Vapor Lock possibilities. I've insulated the gas line, cleaned carburetor, fuel rollover valve on the tank, went and got the latest summer blend of gas again. Right now, mower will start up immediately, mow about 100 ft and stall. I will put it in choke again and it will start immediately and run for another 100 ft and stall.