Ron,
The vendor supplied probe does NOT follow published K type millivolt VS temperature readings. I applied millivolts to the instrument simulating a probe. The gauge followed the millivolt readings within 10*C throughout its full range. The "other" probe produced millivolt reading consistent with its actual temperature. The conclusion is the instrument was fine, the probe faulty.
I had the faulty probe glowing red hot and it would simply not go over 17mv (@425*C) It produced 17mv for a while after heat was removed. THEN began to drop the voltage. Certainly not "fast acting".
I've reviewed my tests with the vendor and they concur and are sending a new tested first probe. I'll let everyone know the results when I receive it hopefully by the weekend.