210 is normal for a tahoe. GM typically uses a 190-195 degree thermostat. This allows the coolant to stay in the radiator long enough to get cooled down otherwise with a lower degree thermostat the coolant just flows thru the radiator with very little cooling and actually cause you to overheat. Many people try a lower thermostat when looking for a overheating problem, some remove the thermostat entirely and then have worse problems. Water boils at 212 degrees, by raising the pressure in the system this temp goes higher. For every 1 LB increase you raise the boiling point 3 degrees so a 15lb cap will raise the boiling point by 45 degrees. 212 plus 45 equals 257 degree boiling point. If you are actually overheating then based on all the new parts you have you need to look elsewhere for a problem. But again 210 is normal and any increase in ambient temp will raise that accordingly.
