I own 2002 Express 3500 w/5.7. I've just had motor replaced for second time due to cracked block where the starter bolts up. When starting, there is a slight hesitation or knock. Motor really shakes. Almost sounds like diesel. It causes the starter to torque and cracks the block after time. The truck has 138,000 miles, but the last two motors were installed within 18,000 of each other. 3 total. Dealer is doing the work but can't seem to find the problem. Any ideas. New motor, new tranny. Don't know what else to replace.