I'm about to throw in the towel and buy a new smoker (realistically that is not happening right now)
Any other thoughts?
Just an idea here, have you ever blown out the burner jets to ensure none are plugged with worms or dirt dabbers or spider webs?
When the burner is lit, does it burn blue or yellow?
Also with all your problem attempts have you been using the same gas bottle?
Another thought, if you are using a newer bottle with the safety valve built in:
If you open the valve on the tank fast it can cause the safety valve to restrict the flow of gas.
Open it very slow at first.......
I have at times, even turned the tank upside down while opening the valve, again slowly.
That smoker looks a lot like my MES electric, with the thermometer on the front door. Are you using anything else to gauge the temp? I was having trouble getting my temp up, even with it on high but for the hell of it bought an oven thermometer to put on the rack. I realized when the door thermometer read 190-200, the one inside was at a perfect 225. Not sure if that's the issue but I wouldn't rely on that door thermometer.