But according to fangraphs pitchFx data, not only his fastball is affected:
FB: 94.1-93.1
SL: 81.2-80.4
Two-seam: 92.2-92.5
CH: 86.4- 86.4
Cut: 78.4-78.7
CB: 78.4-78.7
He's lost velocity on his 4-seam, slider, but added velocity to his Ch, cutter, curveball and two-seam.
The 4-seam and slider to me, are particularly troubling, since those are, after all, his bread and butter pitches (or used to be) since this year, he has drastically reduced the amount of sliders he throws, while drastically increasing the amount of two-seamers and cutters he throws.
He may have lost the feeling for his slider, which coupled with the loss in fastball velocity could explain the inordinate amount of Homeruns he has allowed to date.