Ask Me Help Desk - How do I check air flow between freezer and fresh food side?

I have a 5-year old side-by-side Maytag refrigerator, model MSD2756GES.

My situation:
Freezer side is cold.
Compressor runs (it's hot).
Condenser fan and evaporator fan run.
No frost or snow in the back of the freezer.
Coils on freezer side not frosted over.
Fresh food side is not cold (~47 degrees F).

The adaptive defrost control [adc.jpg attached] was replaced by Maytag in January. That helped for a while, but fresh food side gradually warmed up again. I called Maytag again in April, and this time, they replaced this thing (defrost heater assembly?) [dha.jpg attached]. It didn't help. I was willing to pay for the repair, but I'm sick of the incompetent repairmen and paying for what seems like just trial-and-error repairs.

So based on very helpful information from applguy in other threads, I would guess right now that cold air is not flowing properly to the fresh food side. But I do feel cold air flowing from the vents in the ceiling of the fresh food side when the evaporator fan is running.

To check the air flow, I've just stuck my fingers into the vent openings from the FF side and can't feel any blockage. How can I fully check the "tunnels" between the freezer and FF side? Do I need to take out the ceiling assembly? Do I need to check from the freezer side? What are some other things that could be causing this?

For the time being, I taped a small computer fan to the top vent [fan.jpg attached] and it does help a bit (down to about normal ~37 F), but the cold is not uniform. It's only cold at the top of the refrigerator. The bottom is still warm (which I don't really get since I thought cold air drops).

Also, I understand that there is a mechanism that open/closes a flap in the ceiling vent. For my own education, how does the other vent behind the bottom drawers work?

Thanks for any help you can give me!