I had a 2500 stall converter in a stroker RR, the teeth didn't engage very well the converter,It had bolts the same size as the crank bolts and as such the welded nuts were thicker on the converter, I took the converter back to Hughes in Phoenix, they welded the ring gear 1/4 of a inch forward towards the back of the engine,never had a problem with the starter again,not sure if this is your problem, but it solved mine