Check your fuel system very carefully! Replace both fuel pumps, fuel filter, fuel lines, injectors, the whole lot if need be! 5 years ago, I had exactly the same symptoms you described before some almighty piston meltage! My problem was very intermittent - it was sometimes fine for a few days, then exactly as you describe, so when my fuelling was checked on a rolling road, they said it was spot on and suggested the hall sender. About an after that was replaced, I melted a piston...