Ford Repair: 1995 Ford Mustang, coolant level, coolant system

Question
I have a 1195 Ford Mustang with 112,000 miles on it.  I replaced the head gasket 10,000 miles ago.  My car is running hot in town only not at highway speeds.  My heater sometimes takes a long time to blow hot air if it will at all and sometimes the heater blows very hot air.  Can you tell me what might be making my car run hot in town but not on the highway and if it could be related to the heater not working properly?

Answer
I apologize for the time it has taken, I had connectivity issues. Your problem can be caused by poor water circulation. This can be caused by a low coolant level, or a pressure leak from a heater hose. The heater is a very good indicator of coolant system problems. Look for a leak, if one is not found then proceed with a good flush. While doing the flush, look for a good circulation. Poor circulation can be caused by a bad water pump, a faulty thermostat, or a clogged radiator.