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Heater didn't get hot. Decided to replace thermostat. Discovered it didn't have one. Replaced it. Now truck runs about 220 degrees until I stop at a light. Then it goes up to 260 - 270 degrees unless I rev the engine or get rolling again. Is this normal? What is the normal temp range? "66 250 c.i.

Unless you are boiling the water out of the engine, I suspect you have a bad temp sending unit. Your temp should be running about the same as the rating of the thermostat, most are in the 160 to 180 degree range. Any temp over 220 can be harmful to your engine. First thing to check is the temp of your water. Loosen the radiator cap so it will not hold pressure. Start the engine and let it warm up until the temp is stabilized. Then remove the radiator cap and insert a thermometer that reads in the 160 to 240 degree range, I use a meat thermometer and some candy thermometers will work. When the water is flowing get your temp reading and compare to the dash gauge.

Another possibility is that you put the thermostat in upside down. Spring goes down, on the engine side. If these aren't the problem, you're looking at something being plugged, probably the radiator.

The other possiblity is that since it is cooler when the truck is moving and cools off is that there is an issue with the fan. Maybe a missing shroud, or the fan isn't pulling enough air through the radiator when stopped. Fan stops being effective at about 30 mph.