Bigger beers also need a lot more oxygen or they will stall prematurely, I know this from experience. This is not as big a problem with dry yeast, but more oxygen might help. Also rehydrate your yeast before adding it to the wort. Water allows the cell wall to prepare for the onslaught of sugars, I read an article from one of the big yeast labs that over half the yeast cells can die if not rehydrated first.