Why would my 96 Ford Contour GL have no heat, and overheat after about 30 minutes?

The 96 Contour i have has had an overheating problem before. The thermostat was bad and ruined the head gasket. I paid $1200 bucks to have the gasket replaced and and the head filed down. When i got the car back i replaced the thermostat and bled the coolant system of air. I have checked the coolant lines and completely disassembled the the thermostat housing. I cleaned the housing of any gunk and old build up coolant. And put it back together with the new thermostat and rubber gasket. I have checked all over the engine and underneath for leaks…none. I have checked the water pump for leaks or squeaky barrings…nothing. Have felt the coolant lines for weak spots or cracks…none. I physically blew through the lines for blocks. In fact…it didnt take much air at all to pass fluid. The fluid passed easily. When i start the car it has no problem, the car stays cool for about 10–15 min until the thermostat opens. I have checked both the top coolant lines coming from the radiator to the thermostat housing and the lines are hot. The return line back to the coolant resevoir is hot. Which to me says the coolant is circulating. If im wrong, please correct. But the car still has no hot air and after about 30–40 min the car begins to overheat. The electric fans kick on…but also stay on which im pretty sure is not suppose to happen. But i think this has to do with the engines internal heat not dissipating. Im about out of answers and dont know where to look next with the exception of the heater core. But havent found any reason other than no heat. Would this explain the overheating?