hmm.. check the fuses to your fan.. you said you didn't hear it come on.. that could be why it gets hot when you're at a standstill, but fine when moving.

i'd assume if you were low on antifreeze, even moving wouldn't cool. if you're thermostat was stuck open, and the fans were working, your engine wouldn't overheat, it probably just wouldn't get to operating temp.

if your thermostat were stuck closed (which is very unlikely), it wouldn't cool while moving either.

like i said, i'd check fans first.