I have a rough idle on my 3.9V8. I’ve cleaned the stepper motor. Sometimes even shuts off completely on idle. Also shuts of when put into drive or reverse.
https://youtube.com/shorts/iQ0jJHb7TvY?si=u4mqW6Fo626isJSI

https://youtube.com/shorts/iQ0jJHb7TvY?si=u4mqW6Fo626isJSI
Here is a link to a video I made on the idle.

When you say 'rough' do you mean it's not running on all 8, or just uneven?
If the former I would suspect plugs or leads. What's the mileage?

Stalling when engaging D or R could denote too slow a idle speed. My 3.5efi idles (running temp.) at just short of 1000 in P or N, dropping to 600 when D or R engaged.

If your throttle position sensor isn't giving the proper voltage signal at closed throttle to the ECU the idle control valve won't be commanded to function as the ECU doesn't know the engine is to maintain idle.
Does it idle more smoothly with the air mass meter unplugged?
One, or both of your O2 sensors could be bad. Is the fuel consumption excessive since this issue started?
Check your ignition timing, it could be retarded.
A fuel pressure check is also worthwhile.