I have a 2500 stall converter in a 727 trans. I have been told by a well qualified engine builder the tight converter is causing the in gear idle issues like you say. But I have it working pretty good at this point with the timing locked. I already had the converter before I dropped the stroker in and it was low mileage so I went with it. But if I ever replace it I'd probably go a little higher on the stall.