Ribs didn't turn out the same

You can rotate them every hour or so to even out the cooking.

The 40 will hold 2 racks per shelf, no? Try to keep the on the same level or close. A propane vertical will definitely cook different at different levels. And yes, if you have to go to 3 or 4 shelves then rotate.

I'd love to get hold of a thermal imaging cam and do some testing with it to see exactly what goes on in my vertical smoker in a number of different scenarios.    Yes, there are temp differences between each rack in a vertical smoker.  As racks fill up, the hot spots will change as the airflow in the smoke chamber will be affected.

But, since I don't have a thermal cam, I do what Mdboatburn suggested which is to rotate the meats.   That or not worry about pulling everything off at the same time but rather remove each thing from the smoker when it's finished.  Just did 2 racks of BBs the other day and one rack came out about 30 mins later than the first rack

I've had the same problem getting user to my MF propane vertical.  I've noticed not only the different levels of inconsistency but also that the front of the racks near the door gets a lot hotter as well.  Especially when I do wings frequently, I've noticed the ones closer to the door crisp up a lot faster than the others and I try to rotate them to the back as well as move the shelves around at least half way through the cook.

I've kept my Maverick temp gauge on the 3rd high of 4 racks as well and I am well aware it is not the same temp on that rack as the bottom near the water pan.  Anyone have any thoughts on the best position to put their internal gauge for the vertical cabinets?  Front or back top or bottom rack etc.?

If someone comes up with a thermal cam I would be all about checking that out as well, solve A LOT of questions!

Good Advice !

Gary S