That's somewhat normal for 80% efficiency or lower furnaces, which can have output temperatures at the furnace north of 158F/70C, (pretty toasty!) For condensing furnaces it's usually under 140F/60C, or even under 122F/50C.
Have you tried measuring the temperature? A spot of any non-metallic spray paint on the side of the duct would allow you to measure it with an cheap infra-red thermometer with sufficient accuracy. (Shiny-metallic duct will always read low, sometimes WAY low.)
If the flow is restricted the output air temp rises, and it;s possible that it could be running just below the safety high-limit, which is usually just a snap-disc type breaker/thermostat mounted at the output of the heat exchanger plenum.
