On an older house it's possible the evaporator coil has gotten too dirty over time to allow sufficient air to flow through it. (It's a lot like your car radiator) Probably not the case in your 8 YO house but if the house is in a dusty location it can happen more quickly than average. So if your filters get dirty fast you may have a dirty coil too.
This is what occurred to us 2 years ago.
The coil was well & truly pulgged with hair, dust, etc. It was an amazing thing to see. Once we let it dry out, 80% of it peeled off in great, big sheets of hairy/dusty nastiness. Not something you'd like to see on top of your ice cream.
Our unit was ~10 years old at the time, a Janitrol. (Jani-
junk to one fellow who serviced it.) The truth hurts. It is junk, compared to the sexy new Trane my buddy installed in his place.
Also, the return right under the filter was filled with--get this--
over 80 lbs of busted up concrete & aggregate. WTF, Over? Who shoves more concrete & stone than I can fit into a 5 gal bucket in a return area? It is a pier & beam, for the love of Pete!
When we build a house, I am definitely getting my ASHRAE buddy in on the plans from the get-go.