what should the average temperature be for the gmc denali while driving?

My book shows the stock thermostat (AC Delco) at 187 degrees, So it sounds like it was stuck in the open position, But maybe you should have it replaced before it sticks closed and causes the engine to overheat and you can find a shop here https://repairpal.com/gmc-repair-in-denver-colorado or check thermostat replacement cost here https://repairpal.com/estimator/gmc/yukon+denali