Keep in mind that the temps on the racks are different than the temps on the lid therm. The lid therm could be accurate, and still not be giving you your true chamber temps. If you have a calibrated probe therm do the following:
Cut a potato in half and push the probe therm all the way through it so that at leas 1/3 of the point is sticking out the end.
Get your smoker running at 250° according to the lid therm.
Place the probe on the upper rack and let the smoker stabalize at 250° again - wait untill the probe therm stops going up, make a note of the probe therm temp.
Repeat process with the lower rack.
What you will probably find out is that the temps on each rack are slightly different, and that they both vary from the lid. So once you know what the variation is you can then use the lid therm as a rule of thumb guide, mentally adjusting for each rack.
Also keep in mind the
WSM cooks hotter for the first 8-10 smokes, once you have a nice layer of seasoning built up it will seal all the joints and openings better and not run quite as hot.
All in all you can't go wrong with a
WSM, I have had my 22.5" for several years, I use it year round in all kinds of weather and couldn't be happier!