I assume by Pumptec, you mean a Franklin motor protector and that you don't say what pump you have. If the pump is barely capable of lifting water 600 feet and make pressure as well, it could dead-head when the water level drops. I don't know how well the Pumptec protects against a dead-head situation but it sounds like your pump is no longer capable of doing the job and needs replacement. Of course it would be good to know where the water level is at. If after you pull the pump, when you drop in a new one, tape a length of 1/4" poly pipe to it so that you can use it later to determine the height of the water.