1995 Chevy Suburban engine running hot

i have a 95 suburban with 108000 miles on it? the temp guage is running over 210 now and its winter time here in kansas. i added a gallon of anti/water and can not see any leaks anywere but engine still runs over 210 when driving and falls below 210 when at idle over the summer i pulled the camper and it never went over 210, heat works fine takes about 10 to 15 min to warm up tho and uses oil too!
please help me i was thinking maybe thermastat sticking but had heat so not sure?