Yep it was probe placement... Wow almost 20 degrees? I had the Auber probe toward the back and that was a cooler temp than the one that was place toward the door both hanging in the middle I only have one grate in and it's near the top so nothing by the probe. What is the better placement spot?
Probe placement is everything. It's not necessarily that there are hot spots in these cookers, but the walls radiate differently from the racks, which is different than any temps by the meat. The temps below the meat are drastically different than temps above the meat.
As for placement, I would say pick one and keep it consistent. The consistency will help you more than the accuracy... if that makes sense. Look at any $5000 competition cooker. They have a couple of fixed thermometers. They "learn" their cookers based on those thermometers and cook accordingly, despite hot spots.
I use a chuck of wood with a hole drilled through it or a ball of foil, stick my probe through it, and place it on the same rack as the meat, as close to the middle as I can, while trying to stay 2-3" away from the meat. I'm not sure how accurate that temp is compared to the rest of the cooker, but I cook to that temp.
Glad you got it figured out.