1999 Chevy Tahoe temperature

I recently replaced the radiator and thermostat. Yesterday I noticed that (while running parked in my driveway) apprx 1 oz of antifreeze leaked from the auto. (not sure where it was coming from) fluid levels were ok at that time. This morning I drive in to work (roughly 30 miles) and the temperature gauge goes from 160 degrees to 235 degrees.... then back down and up to 250 degrees....

any ideas???

Thanks