I bought a 3 pack of St Louis style ribs at Costco.  Did a single rack at a time and used the same 3:2:1 at 225*.  The first two racks were very much the same result.  The third rack done this past Sunday were not done to my liking.  Did not pass the bend test after 5 3/4 hrs and at 6 hrs were still not as tender nor did the meat pull off the bone well.  Now they did taste great, but I am amazed that they were not done the same. My conclusion:
Not all pigs are the same even if raised the same.  Checked the Stampede and the temp set is right on the mark. Used the same pellets, weather was nearly the same. ??

Probably not related, but did some of the racks still have part of the riblet attached? I've been disappointed with the STL's from Costco lately due to the way they are cut with part of the tips still attached so you end up with bits of cartilage in your mouth. Not sure if it's just sloppy work, or the producer is trying to maximize production. I think the producer was Hormel, but not certain.