If your not seeing any running concern, stalls, chances are your cat is fine. If it broke up it could make restrictions in the mufflers. As for the temp, the thermostat is metered and you will see fluctuations over 210 as well as under. Your fan will not kick on untill 225-230 degrees depending on how accurate the resistance is read. I'm guessing at 60 mph your running at 2000 + rpm? If so, your current fuel mileage is where it will stay. I've never understood why GM does the things they do, or any manufacturer for that matter. I am curious what you get for fuel press.
