Ron, that sure is a beautiful tractor....and I recognized the grill when I saw it. Maybe I should ship you mine and have you work it over.
Are you running the offroad fuel....or the tweaked up winter variety from the gas station? If offroad, you might try switching, or using an additive.
Also, have you thought of going to a synthetic oil? Might be more fluid in the cold weather.
I have been very pleased with my 4020. I am on the 2nd winter now...although we have about 50 degrees outside now...we got down below zero 3 weeks ago. I just do one cycle on the glow plugs and she fires. It has been very dependable so far.
I just hope I haven't jinxed myself...as we are supposed to get to single digits by the end of the week. My tractor sits outside in my temporary shelter (tractor tent or igloo). I might be humbled if we get down to 20-30 below....but that doesn't happen often. I've been running the on highway fuel, keep my tank topped, and use synthetic oil.