With old thermocouple pilot flame would hit thermocouole perfectly and with plenty of flame as I would try to get pilot to stay on. I repeated a full 60 second attempt 5 times in a row. I figured a had a bad thermocouple. Replaced the thermocouple and have the same results. Could it be a bad gas valve and are there any other possibilities anybody can think of?

Found the problem. There are two wire terminals located by the thermocouple port which say E.C.O.. Evidently that stands for emergency cut off. I disconnected the devive that was attached there which is the High Temp. Limit Switch and put a jumper across them and finally the pilot light stayed lit. The limit switch only had continuity periodically. I cleaned the terminals with some emery cloth removed the jumper and presto, it's working again.