Deck threw 91-93 with a straight fastball. The slider was supposed to be plus and the change was supposed to be a ~50. All of his scouting reports praised his command and mound presence as plus "tools", and said things like, "has shown the ability to get by without his best stuff", "all he does is win".
I've read that Harris' FB has movement and can touch 94/95 right now, and the body might still have a bit of projection. Also, it seems like his 3 offspeed pitches all have 50+ potential.