Ok.. Interesting experiment.
I noticed on the heater tube breakaway diagrams that the heating elelement is much closer to the sensor on one side, and less on the other. In a low flow environment where the water flow was travelling in that direction may be slightly warmer then the other direction. So I removed the heater and installed it the oppoiste way.
Immediately my temp readings dropped to within 1-2 degrees of each other and no more HL/DRY errors, even with filter installed again. WIll post results as tub warms up, but that has made a difference for whatever reason..