Chevy Misfires

I have a 2000 Chevy Silverado 1500 4.8 liter with 96,000 miles. I have severe misfires on cylinders 1, 3, 5. I have replaced all wires and plugs and replaced the ignition coils on 1, 3, 5. I still have problems getting the engine to fire (it turns over fine) and when it is running I get several hundred to several thousand misfires on those cylinders. Any idea what else could be wrong?

Possibly a bad ignition module. This module converts the signals from the computer to tell the coils when to fire.

Any idea the cost and if there is a way to test it without replacing it?

Could it possibly be the fuel pressure regulator?