I know very little about big trucks but I found this very cool:
Apparently Mack trucks are made in Macungie up near Allentown, not far from RTHQ in PA.
Used to be the sole manufacturing plant for Mack. Had relatives that worked for them.
In the 80's or 90's they moved most of the manufacturing to South Carolina if memory serves. If any production is still in place in Macungie, I would expect it to be low volume.
Mack originally had their manufacturing in Allentown. As they needed more space, they moved out to Macungie. I was under the impression that Macungie is now their spare parts distribution center but no manufacturing is being done there. I may be wrong.