My 1992 caprice is having trouble passing California smog check

My 1992 caprice is having a hard time passing California smog check before I took it in I had replaced spark plugs and wires oxygen sensor throttle position sensor coolant temp sensor map sensor air idle control valve and it failed there was a check lite on it only comes on now when I run it hard or on highway after car has been running it seams like its guna Die but sometimes will spudder and almost die but will kick in after a few seconds then I had timing checked it's dead on 0 zero so I'm at a lose her can you help the converter looks and seams ok that's like the only thing I haven't replaced