That kind of work should have been done in the offseason and maybe it was. If he's being sent to AAA to rework his pitches at this point then something went seriously wrong.
He's tightened up the slider a bit and is throwing it a lot more often in his 5 innings, with good results and way more whiffs. He's struck put 25% of batters too, for what it's worth.
I want to see what we have in Pop, I think he might be a big part of this team.