Hi @bko , and thank you for your insight.
I thought about buffering the thermistor, but in reviewing other designs that incorporated the ET-73 probes I'm using, it looked like one wasn't needed (even for the core).
@avidan is using the same probes, and it appears his ADC readings are more on par to where mine should be. The only difference I can see, is he's using A4 instead of A6; however, that shouldn't be an issue. I'll try A4 later tonight to see if it make's a difference (I wanted to leave the SPI ports free for future expansion). In the meantime, can you think of any reason my readings would be so far off from his? I wired my core exactly like he shows in post 11 of that topic, with the exception of using pin A6. My fixed 22K R measures out at 21k6, so I don't understand why my readings are way off.