I think you have nailed it. I have been thinking that my air flow at registers was getting to be lower. It happens slowly so you almost don't notice it. Will let you know when I have completed task.
Thanks for help.

The furnace is probably 11-12 years old and yes it has an a coil in the lower compartment. Are you thinking it might be somewhat clogged? That thought has also gone thru my mind.Any way to clean without pulling the a frame? Could I use low pressure air to blow out and I have vacuumed the top surface...

I am using the factory washable and have replaced with new.

I have a nordyne miller m1mb 077a bw The furnace starts and heats up and the blower runs, but before the house has reached the target temperature the furnace shuts down. once I saw a 1 blink yellow which says open limit switch. I replaced both switches and it ran for a long time. Then it started to ...

Just ordered and received new capacitor p/n 622133 and not sure if it is polorized. Don't see any markings anywhere on it. Is this just put leads on any of two terminals. furnace is Nordyne-Miller m1mb 077a. Also is the blower assembly heavy? It looks like it has to be removed to get at area to repl...