Don---got to ask a couple basic things---did you use new GM starter bolts on each starter? ( they have a knurled section that makes the alignment tight) and the flex plate wasn't on backwards???????? Was the main bearings align bored (changed centerline?)

I'm dealing with gotta replace flex plate on my 1999 Ford F350 with 7.3 diesel --chewed up teeth after 320,000 miles showing on odometer but it didn't work for 6 years so probably 450,000 + miles