This is an Amana furnace 80% efficient with a heat rise rating of 30 to
60 degrees. Can't remember the exact model number. Installed in 1999
IIRC.

I'm using the infrared thermometer to measure the temperature of the
inside of the register boxes about 7 minutes into the 10-minute cycle.
The air temperature should be no more than a couple degrees hotter at
that point.

75 degrees is fairly accurate. Given the cheap IR thermometer, it may
be a couple of degrees off, but that's about it. My main complaint was
the cold drafty feeling instead of the warm cozy feeling every time the
furnace kicked on. Now that I've got the heat rise back, I've got the
warm cozy feeling back. But I've got all the registers but three
completely closed off with the dampers down in the basement.

The house is warm enough to suit me, but there is a 7 degree difference
in temperature from the living room to other rooms in the house (72 vs
65). One of the registers in the living room is completely dampered
off, and the other one is wide open now, but damping that one doesn't
seem to make much difference. Living room is right over top of the
furnace and main plenum, so I expect some heat transfer happening there.