Yesterday (INDEPENDENCE DAY) I smoked 3 racks of spare ribs in my 40" upright masterbuilt propane. One rack was "fall off the bone" quality and the other 2 had good flavor as well but were tougher. I didn't notice until I went inside to cut them and serve that one was much better than the others. I'm thinking that the one that was on the lowers most rack was the most done. What do you guys with upright smokers do to prevent this and I'm guessing even heat throughout? My thermometer is an aftermarket and calibrated. It's in the top third of the cooking zone.