What temp did you set it at exactly?

A total convert seems a bit strong for a post driver. I get it saved you some time on that one fence, but it's just a heavy tube. For a couple posts I'd still just use the back of my digging bar. Maybe if you're doing that kind of work every single day it makes sense.

Oof, that's a rough one. Actually, letting the board dry for a full day might not be enough in a cold, damp basement. You really need to check it with a moisture meter first. I've seen guys rush that step and the new mud just fails again. A slower setting compound is the right move, but the prep has to be spot on.