I think the addition of the "J" on his jersey is throwing off his balance. The extra weight on the left side of his body is likely affecting his ability to maintain power through the 2nd half of his swing.
All kidding aside, I'm not sure Manny coming back will be much of a factor for him (Ethier is another story though). I could be wrong and the team synergy will motivate him to get those #'s up, but I'm not sure. This seems to be just another example of why you don't draft a catcher early. I took him in the 4th round in a 10 teamer. Right now he's ranked at 645 by yahoo, which is atrocious. He's on pace for a career high in K's. Still 0 HR. I'd be content if he can get his average up from the current .250 to his career avg of .280. I don't think he's even trade-able right now. The only plus is the 7sb so far.