Went back with both thermistors and the control board today. It was actually working worse than the first time I looked at it so it was much easier to diagnose. I could jiggle the cycle selector knob and get the display to flicker between the correct time and 20 minutes. I pulled out the control board and resoldered all the selector switch connections. Put it back together and now it works great. Saved my customer the cost of a $300 control board so, needless to say, they were very happy.