Yea if the engine was running fine before install, its not the engine.
Not saying anything bad about you either. I am a Mechanic and small things do get missed.
i.e. Did an engine swap on a () Integra and forgot one ground behind the intake mani. Car would start but not run, took 2 hours to find that one wire.
Just give it a good once over. You might find something small.
I'D RATHER PUSH MY FORD THAN DRIVE YOUR CHEVY
MM COBRA CLUB #124