My family and I moved into our new home 3 months ago. Turned on the heat and the end of October and my wife who stays home with our toddler age kids noticed the stuffy air in the basement. I reached up with my hand against registers and the airflow is really low - probably less than half of what it feels like on the main level.

We had a heating tune-up, seasonal checkup done yesterday and were told the furnace runs well - no issues. The filters are clean.

We also had a contractor today who inspected the ducts - the main supply duct and the return down in the utility room. He said that he could not see any dampers on the main supply duct (that goes up from the furnace leading up to the main level and branches off horizontally to the basement). He also said that he thought there may be registers that have been sealed off inside the drywalls; or some other problem that's restricting airflow velocity. He did not perform additional in-depth testing.

This is a Winchester Homes colonial type SFH built in 1999. The basement was finished by the previous owner after they initially bought the house.

Is there a cost-effective way to repair this problem without opening up drywalls to locate a potential area of air leakage or airflow being restricted?
Do you know of any specific tests or equipment that can be used/installed to troubleshoot this problem?

Your advise is much appreciated!

Rheem gas furnace 75000 BTU's/hr. 80 AFUE.

Thank you very much!