I loved those photo and I'm sure they were a great draw for someone to want to ride that line.
I don’t really see any fault regarding the Trainmaster.
I would suspects all the cause of the stall was account the sanders not working properly. If they were dropping way too much sand, they were sanding the wheels on the entire train and there can be no more drag than that in a train. Sand on all the wheels going through all those curves on that line would be just like putting the brakes on the train while going uphill. Sand is only useful for the locomotive adhesion, but it is damage when it gets back on car wheels. I know water is too scarce in that area to have rail washer installed on the lines locomotives. Some railroads have tested the use of water washer to remove grit and the water lubricates the following train wheels. Curve greasers of the flange area of the rail are the general practice to aid that problem.
Those lucky passengers got a rare ride that will likely never happen again. I bet Carlos felt the luckiest to get the chance for a little more steam after his boring Railrunner lever pulling.
Another question, when a train crew ties down a train in this case on a very steep grade, does he walk to the rear freight car at the tail end and apply hand brakes on a sufficient number of cars to hold that entire train which included loaded passenger cars? Or are hand brakes only applied to the passenger cars and none to the tail end freight cars? I would believe that a sufficient number of brakes applied would be quite a number of cars to require hand brakes cranked up because of that very heavy grade.