As I said in my previous post, I did start with an entire chimney full of full engaged KBB and then added a full chimney of unlit on top of that. Perhaps I just didn't let the unlit engage quite enough, but when I first assembled the cooker, it was able to hit 280 and then if I left the access door open, it could spike up to 350. ...
I apologize, I missed this earlier. Try dumping the lit coals on top of the unlit; maybe that will help. And let the fire engage a little longer so that you are starting at over 350 when the cooker is assembled.The temp read about 345 when I assembled the WSM, fell to about 300, and slowly fell to 286 even as the Pit Viper was blowing as much as it could.
I looked at the bbqguru website. On the page for the Pit Viper (medium) Fan, I could not find a specification that indicates its CFM. But I did notice something in the photos. That fan has a thin metal tab that sticks out and is labeled open and closed. Is that metal tab slid to full open position? I apologize if you have checked that. Even if that tab is set to open, set up your guru without a fire in your WSM. Put your hand into the bottom bowl of the cooker where the fan blows in. Do you feel any airflow when the fan is on?
What was the ambient air temps during your cooks?
Have you reached out to BBQ guru for support?