Head gaskets going bad will either use coolant and steam out the tail pipe (smell to), or blow coolant out of the radiator overflow. Pull the radiator cap when the engine is at idle and watch for bubbles (not the monkey!) in the coolant.
Fan should be in the 3/4" range from radiator core.
Sounds like air flow problems, since it cools down when moving. I assume you are using stock pulleys? Plugged radiators generally heat up out on the road and can't get rid of the heat through air flow. A lean carburetor will also heat up a engine pretty fast along with a plugged exhaust system.
Get a infrared heat gun and check the thermostat housing, block, head, and radiator to get a idea of true temp of the coolant. Also get a candy thermometer in the neck as a back up. You should see no more then one or two degrees above T-stat temp.
Mine reads about 20 hotter then it really is using the OEM hole between #1 and #2 cylinders. I moved the probe to the T-stat housing and now the gauge read actual coolant temp, 190 right on the money.
