why does temperature gauge fluctuate from nearly over heating then back down again?

Check anti freeze level making sure it's not low.

already did that and its still doing the same

If your antifreeze level is ok and ur cooling fans are kicking in normal you may have sticky thermostat. Can you hear the cooling fans kick in when this happens or are cooling fans already running?

the fans are going....do I need to replace the thermostat?

Yes

ok....thanks

If vehicle is actually not over heating you may just have a bad coolent temperature sensor or like Irodri911 suggested a bad thermostat stuck in the half open and have closed position or a clogged cooling system that needs to be flushed.