That chart helps a bit. But the oddest thing is this:
He pitched 5 innings (82 pitches, a little high, yes) 6 games ago. After that start, he was down to a 72, since then he's only gotten back up to an 89. In 6 games.
When he would only throw 20-25 pitches in relief, he would go down to 88 or 90, but it would take 4-5 games just to get back to 100. Seems too long to me.