98 PCM

Do you need a ”replacement“ because the current PCM is damaged/inoperative?

Or are you looking for one with a upgraded or custom tune? If it's the tune, your existing PCM can be programmed while in the car, or by a mail-order tuner. Is the engine stock or modified?

You have non-stock injectors? And what is the extent of “the obvious that I've changed”? Are those performance upgrades?

Have you done a compression test?

PCM failures are extremely rare.

We’re you getting a fault code for #7 injector?

Were you able to used a code scanner with GM “enhanced parameters”? Is that how you accessed the misfire count for #7?

Not sure why I'm asking these questions since you've already made up your mind it's probably the PCM.

P0307 indicates a misfire on #7, doesn’t indicate the cause.

Random misfire due to compression - faulty lifter, sticky valve