When you turn fridge OFF ALL DC power to control system is shut off so the only way the main flame (no pilot flame) is staying lit is because gas valve is not closing.
Your thermistor and lower board where not the problem......gas valve is.
The 'auto thermostat' (non adjustable pre-set at factory) is what controls fridge cycle via temp sensed by thermistor. The thermostat turns heating source (electric or gas) on/off to control fridge temp.
You can make minor temp adjustments (6*-8*F) by changing position of thermistor on fin.
Move thermistor clip up for cooler
Move thermistor down for warmer
BUT with gas valve not closing.....main flame continues to burn causing excessive cooling
Time for a new gas valve....part #2932615012 About $125
Is it time for your medication or mine?
2007 DODGE 3500 QC SRW 5.9L CTD In-Bed 'quiet gen'
2007 HitchHiker II 32.5 UKTG 2000W Xantex Inverter
US NAVY------USS Decatur DDG31