1995 S-10 Blazer - Engine partially turns over, won't start

Chevy S-10 Blazer 1995 100,000 miles Vortec V6 auto trans.
Initially thought it was the starter, replaced starter and battery and still would not turn over. Thought engine was seized, was able to rotate the crank manually then tried the ignition again and it partially turned then stopped as if it jammed up against something internally. Before all this happened the driver mentioned the engine revved to 2500 rpm and smelled of gas. Any thoughts or suggestion for next steps to troubleshoot?