Like Dave, I rarely add liquid in to the smoker these days. In the past, I would smoke everything at 225*, and baby backs would go almost 5-6 hours, but I’ve bumped the temps up on my cooking as of late with great results. Saturday, I went with 250* and the baby backs were out and wrapped in foil right at 5 hours. I probably could have pulled them a little sooner as well.
What temp have you been smoking on the four cooks? With one of the cooks turning out good, it could also be the ribs? Sometimes meat just acts differently even with the same cook process.
Hope you enjoy those STL ribs!