Well,I'm no expert,but I have cooked a few in assorted Cookshacks.
I haven't had the chance yet on an AQ,nor at high altitude.
Most folks would consider themselves fortunate to get a packer in Ca.
Stores can usually order by large ,or small case,as well as the seasonal issues.
Sometimes smaller "could" come from younger animals,which sometimes can be more tender beef.
Moistness may well come from the quality/grade of the packer and defy cooking technique.
We find internal temp to be an indicator of when to start poke testing a packer.
My extremes have gone from 186º to over 212º.
Rarely,do I get one to come tender at 190º,but other cooks do.
Brisket is usually considered the most difficult product to cook well consistently.
Practice and some percent of dissatisfaction are the typical keys.
Did you try adding a cup of beef broth/black coffee,etc to the foil you let it rest in?
Just a couple of thoughts.