The only time I've seen similar on an I6 was when the pickup coil on the distributor was bad. It would still spark, but not enough at the right time to fire.
You know, you only need compression, spark and gas. You should be good w/those. I would take a stab at that pickup coil. If I remember right they are only about $13-$15
Or, you could have water/condensation in the gas. Crank it over for a few, pull plugs and look for small droplets on the plugs. Gas spreads evenly, water forms droplets.