Steve,
Sure sounds like incoming air temp or lack of airflow. When driving, the incoming air is already heated by the pavement which you can't duplicate by running in place. I'd verify a clean radiator, and tight belt per Ed. Also, check on any work done recently that might change the airflow under the coach in front or near the gen set radiator.
I don't understand why the gen set keeps running at 230. While I don't have the manual, I would think this temp would trigger a shutdown and cause it to flash an overtemp code.
Steve