Personally, with a dog like that (and I don't speak from experience, Pimg was quite easy to train) I would revisit BOTH grid work AND one jump work. The one jump is very important because it teaches him how to read you. It teaches him that your timing can be off and it doesn't matter. It allows him to see different pictures of the same move (FC, RC, etc) in a small, controlled environment. I would think such training would be equally as important, if not more so, than grid work.
Grid work should teach how to jump while one jump work teaches how to read the handler during a jump. If the problem is handler induced, I'd be revisiting one jump work.
C-ATCH Pimg - DOB: 2/06, RATO, UJJ (x2), DJX, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014
RATCHX2 High Jinks vom Neuanfang - DOB 9/12 (Gotchya Day: 1/23/2013) DN, CA