1997 Firebird Random Misfires Multiple Cylinders

1997 Firebird, 135,000 miles. I bought it 1 1/2 years ago. It has always had a P0441 error code that has to deal with emissions evac system.

This week it started missing really bad and gave a P0300 Random Misfires Multiple Cylinders code. I had a similar one a year ago, but it was only two cyclinders and I fixed it by replacing the Ignition Coil. I replaced the other two and it ran great.

Two days later it ran bad again. I replaced the plugs and fuel filter. It ran great again. A day later it runs bad again.

At Autozone, they suggested the Ignition Module or Injectors. I don't want to dump in another $150 to $500 bucks on guesses.

Any ideas? This is my daily driver for work.