Georgetown Steel used similar Macks to haul out the slag pots when I was in there in the early '90s. They had been there since the mill started up in '69, and are probably still operable. They aren't running the furnaces now since they are in a legal battle with the city, who rezoned the mill property for condos and declared them noncompliant with zoning.
I did see one of those snag one of our R-models, loaded to about 90,000 lbs, and pull the cab clean off, then drag the whole truck 100' or so. The guy in the big Mack never knew he had it.