MB ML350 engine stumbles when stopped at light

Hi,
I have a MB ML350 of 2003. I have this weird problem with my car for a year now.
When I stop the car slowly at a stop sign or light, the engine stumbles randomly when car comes to the halt.
It feels like engine might just stop any second now but it never does.
The engine sounds like panting as if its starving air/fuel, missing strokes (the sensation at steering wheel) in between.
If I press accelerator to rev the engine, car takes almost a second to react.
Under normal conditions, car reacts much faster to revving.

I noticed that when it happened, the car was recently started from cold and engine was at much lower temperature.
Also, the RPM needle would drop a bit when engine stumbled. The car is always in ‘D’ and putting it in ‘N’ did not stop it.
Can there be some issues with fuel injector or something?

Car has gone through regular maintenance of oil and filter changes in past 3 years by a trusted mechanic (the years I owned it).
Has anyone seen similar behavior? Is there any tests I can run to narrow down the issue?
If yes, any estimates on cost of repair?
Thanks in advance.