2000 Chevy S-10 Missing Bad

I recently started getting bad gas mileage and I then changed the spark plugs and the air cleaner. I was still getting bad gas mileage, so I used some Chemtool injector cleaner to see if my injectors were clogged.

Shortly after that, the engine began missing.A little at first and now terribly. I then changed the fuel filter (california emissions style) and there is no change. The check engine light did, however, come on when it started missing really bad.

What do you think?