After running Dash's test, I determined that I had negative pressure in the house. I found an open seam in my basement return ductwork, which I sealed. The basement has no supply/return registers.
I am thinking that adding an additional (first floor) return would be relatively easy, and would improve airflow to a couple of upstairs registers.
After thinking about it, other than the size (larger) of the proposed return compared to my former leak, wouldn't that cause a negative pressure in the house (all else remains the same)?
I've read here, courtesy of Beenthere, that reducing return static might cause an increase in supply static. But, in the past, one contractor I interviewed, cracked open the blower door on my (non-ECM) furnace and the airflow to those areas was vastly improved.
My present furnace has an ECM blower. So, what's right and what's wrong?