Back in spring training, there was talk coming out of Marlins camp that pitcher Josh Johnson(FLA) was tinkering with a sinker. PitchFX has yet to track any sinkers from Josh so far this season. However, he's off to a tremendous start with a 3-0 record in 4 starts, and a 1.00 ERA and 0.593 WHIP. Part of his great start could be due to his ability to keep his pitches down consistently.
Josh has successfully managed to locate his pitches away to both lefties and righties so far this season. Against RHB especially, he's sniped that down and away zone very efficiently. In 36 plate appearances, opposing right-handed batters have hit only .086 versus Johnson with a 36.1% strike out rate and a 2.8% walk rate. Against 61 sliders so far, opposing righties have not managed a single hit.
For now, adding a sinker doesn't seem necessary for Josh Johnson.