Does this indicate an overheated or overworking furnace?

Before making any judgements, learn more about furnace parameters by reading
DIY books, tomes on HVAC, whatever you can find at your library, box store or
whatever.
For example, many furnaces operate with bonnnet or plenum controls that cycle
between 140 and 180 dgrees F.

ducting coming directly from my furnace is extremely hot to the touch. It's
hot enough to burn if the finger is (sic) left there.

Since the body can tolerate temperatures only around 140 degrees F your ducting
may just be near the normal upper limit. If your research doesn't answer your
concerns, call in a qualified tradesman for a system service and let him know
up front that you would appreciate learning more about your heating plant. Be
aware that his time is money and will be reflected in your bill. Be a gacious
host and offer a danish and coffee before he leaves. Good luck.

Joe