I can only imagine how exhausted you were after a 3-hour tour. We were only in Mexico City for 4 full days and my lungs never got used to the elevation and air pollution. I am not in the best shape of my life by any means but that air sure slowed me down.
Yeah we were really tired!! And the air pollution was definitely getting to me towards the end of the trip... My eyes were getting a little irritated from it.