My brisket flat went from shoe leather to buttery after one $8 change

I smoked briskets for about 4 years and every single flat came out dry and tough, no matter what I did. Last month I finally bought a cheap oven thermometer and hung it on the cooler side of my pit, turns out my built-in gauge was reading 40 degrees too high. So I had been cooking at 265 instead of 225 the whole time, which explained the crumbly texture and the 2 hours shaved off every cook. After adjusting to the real temp and adding 45 more minutes of rest time, that same grade of brisket sliced like warm butter. I almost threw that $8 thermometer across the yard out of frustration that it took me that long to check. Has anyone else found a tiny equipment fix that changed their whole cook schedule?