Ok. I went ahead and restarted X-Plane, and started a fresh new flight at KTEX. It remembered I had left TerraMaxx on mild winter. I'll just make an assumption that my load situation caused it to load off earlier. (No Idea why it didn't stick initially, works now) Go ahead and try auto again. Loads up summer. METAR still -6*C. I'll have to just do manual mild winter for a bit I guess. Weird that it's loading summer.
EDIT: Further testing today, loaded up KGUC. It's -16*C, try auto again with -2*C for the deep winter cutoff. Loads up mild winter. Figure it should be deep, but it does at least load winter this time. Then I goto the plugin folder to poke around, open seasons.txt config, and notice the WINTER MIN N LAT is 1 tile further north than KTEX. Go ahead and change it from 38 to 35 for testing, plus I know tiles in the +35 that get snow. Load up KTEX again, -11*C, loads up summer. Restart X-Plane, and with a fresh plugin load, loads up mild winter. I'll definitely tweak seasons.txt to my liking.
But still mild over deep, am I too close to the winter cutoff border? Load up KBZN, -14*C, still mild. Fiddle with the deep winter cutoff slider, hit +2*C, loads deep. +1 stays deep. Stupid mouse blows through 0, -1 loads up mild. Get it on the default 0, loads deep. Am I misinterpreting the function of the deep winter cutoff? For now I'll just leave it on the default setting.