It's a rule of thumb when replacing thermo's to replace them in pairs unless you want to reopen your machine everything a thermostat or cut off burns out..............Change the burner chamber in pairs as it comes in a kit and if you haven't changed the operating thermostat next to the thermal fuse it'd be wise to do it because that may be your culprit. As you said you have continuity in this but didn't say it's infinite on one leg and low resistance on the other as it should be and if it's not or rattling excessively replace it this is one of the most important parts in regulating the temps. Before you replace all the parts measure the voltage at the heating element you should have 240 if you don't you may have a wire or timer issue. Also you never stated whether or not you checked the ventilation out of the unit a clogged or semi clogged exhaust line out of the house will cause this because of backpressure messing up thermostats. Go watch some more video's you missed some steps in diagnosing that will help you.