Could be a plugged fuel filter and/or line. When it starts to die, choke it and see. If it acts like it wants to keep running,probably fuel problem. A coil/condensor will work when cool and when it heats up it will stop firing. I would be led to believe that if you were having a vapor lock problem, it would be after the vehicle has been run for a while(not just warmed up) in very hot outside temps. You're in Tejas, so it could be true. Vapor lock occurs when the gas boils and turns to vapor. Motor won't run on vapor. Easy way to check is to wet a towel and wrap it around the fuel line with tape before you start it. If it still dies after warmup, replace the coil and/or condensor.