Rough idling, RPMs fluctuating and stalling?

Regardless of cold/warm start, the engine will have a rough idle when the engine lowers to the operating value. While driving, the RPMs will continue to bounce around when I apply light pressure to the gas (maintaining a low speed in the OD gear). Most of the time it runs fine when accelerating but does have these “random fits” of backfiring while driving that are sporadic. And the engine is very unhappy when switching between drive/reverse when I’m going to park (lots of RPMs bucking and can choke off).
The problem started about a month ago. To this point, I’ve replaced the spark plugs and cables (AC Delco), rebuilt the throttle body (AC Delco rebuild kit) and installed new injectors (refurbished).
I’ve done some research and I’ve come across people experiencing similar issues and it ended up being solved by replacing the ignition control module or the ignition coil.
Looking for assistance/advice. Is there a way I could verify both of those with a multimeter? Or another way? Could it be something else?