2007 Pontiac Grand Prix PONTIAC IS RUNNING HOT

I HAVE A 2007 PONTIAC GRAND PRIX . IT RAN HOT SO WE REPLACED THE WATER PUMP AND IT SEEMED TO FIX THE PROB. THEN THE TEMP GAUGE WAS GOING UP MORE THAN NORMAL SO WE FLUSHED THE RADIATOR AND PUT DEX COOL BACK IN. NOW THE TEMP GAUGE IS STILL READING HOTTER THAN NORMAL. NOT RUNNING HOT UNLESS IT SITS IN PARK FOR ONLY A FEW MINUTES. PLEASE HELP AND THANKS