1989 Lincoln Town Car overheating

I have a 5.0 liter engine that in the last 2 years has a growing temperature problem. Radiator replace. Not losing any coolant. Proper coolant in service. Heater works well. Have changed thermostats 3 times 180 degree. Changed water pump twice. Changed fan and fan clutch. Oil and water NOT mixing anywhere. So the problem is that the engine temp has been running higher than normal under same weather conditions for the last 2 years, progressivly getting worse. I can tell by the heat off the engine this to be the case, so I don't suspect the temp gauge. In traffic the temp will rise to barely under the HOT mark on the gauge. Out on the road it will get some air and cool back down to the range it normally runs, as it did 3 years ago- needle between the A & M on the gauge. I have run it scince july without a thermostat. Even without the thermostat it runs pretty high on the gauge in traffic. Then will cool back down out on the open road BUT will not get back down to running where it should be. I think maybe there could be a blockage of water flow in the block, however my local mechanic did not recomend a flushing of the block. Transmission coil is not blocked and the transmission runs normal. If the engine block has a blockage can I flush it myself, and how do I find out if the block has a restriction? What do you think? Thanks for the help. Edward Higgins