I have a 02 Grand caravan that has new radiator, termostat, one new fan. the temp gauge goes up to max hot the drops right back down in seconds. what could be the problem?

It could be you have an air lock in the cooling system
remove the rad cap from the rad, start the engine and let it run until the coolant drops (add to fill it back up) or until the coolant boils out of the rad spout.

maybe pull the heat sensor. -replace it OR clean it off, reinstall it.

A lot of thermostats stay shut till operating temp is reached , then open in one movement , this is what happens, temp gauge goes up to hot, thermostat opens , cold water from radiator enters engine, temp gauge drops to cool, coolant circulates becomes worm . gauge raises to nun , every thing ok. Some thermostats are fitted with a bleed valve to over come this sudden movement, I have been known to drill a small hole in the thermostat so the coolant worms slowly.