Well we bought this 99 blazer and it needed a motor. I had a 2000 S10 with a broken frame so I transfered the motor. Then the starter went bad. So I went to autozone and purchased a lifetime warranteed started that lasted 2 days. Next the motor broke where the started connected so I purchased an 03 motor with 57000 miles on it and the started problem persists. I have changed the started 6 times in the last week. I took the original started and had it rebuilt twice and exchanged the other one 4 times. I'm at my wits end. It will start once with each starter change but it takes forever to start and then it burns the starter out.
The only things I have ever seen causing multiple start failures is a bad crank sensor. Sometimes when they go bad, the engine will kick back and can actually break the starter nose off, of just cause it to not crank anymore. The other is cheaply made parts. But, with so many, I would not think that is the case.
At the end of your post you said that it takes forever to start, then the starter burns out. If this is the case with each engine- that it cranks and cranks and cranks, then I would be looking at a bad fuel pump with low pressure. But, even a decent starter should be able take multiple extended crankings without burning out.