Hello jremington,
Here at home I'm at 600ft ASL (so should be about 99.3 C I reckon) and my thermo peaked at 88.75C, but at my previous test I was only at about 40ft ASL and the thermocouples still read only about 88\89C in a boiling kettle - then I had a calibrated Fluke in there too which read a shade under 100C.
I'm stumped.....!? My next test will be to use a different make of breakout board as that seems to be the only common factor.
Thanks