my 2004 v6 4.3 savanna van will turn over but not start got good spark and gas

Had it scanned? Check entire air cleaner for debris from mouse nest. Make sure mass air flow sensor has NO trash on it! They seem to like this vehicles air cleaner assembly. Have had 2, Savanna service vans, in the last month with this problem! Also do the basic no start test, spark and fuel PRESSURE! I have seen the distributor assem. slip, out of time, on these vehicles and cause this! Check engine light should be on and needs a scan test!