If you have access to a Manometer, RISEPRO Digital Air Pressure Meter and Differential Pressure Gauge HVAC Gas Pressure Tester: Amazon.com: Industrial & Scientific you can test how much static pressure is in your system. There are many tutorials on youtube that will show you how to do this. It's pretty easy since all you need to do is drill a hole before and after the blower and take pressure readings to calculate the total external static pressure. If it's too high you definitely have a return issue. I have a 20x20 return grille with a 4" Honeywell filter on my Trane furnace in my 1300 sq ft home and I'm running .5 static which is ideal. It appears your return is too small.

Unfortunately, many installers don't even own a manometer and use rules of thumb to size systems. The most effective way to design is with a Manual J calculation

Your return and filter should be able to accommodate 1000 - 1200 CFM of air flow. The AC is probably oversized also.

It's a bit more complicated than simple duct size as static pressures enter the picture as well.

Generally you want 240 square inches of rectangular duct for 2,000 CFM and you have only 160. However, your system is not actually doing 2,000 CFM as static pressure (including from the small return duct itself) reduce CFM's. A good (and they're difficult to find) HVAC person should be able to tell you what you need for your house size, infiltration rate, insulation factors and environment.

One comment - 1" filter? Your filter is larger (400 sq inches?) which is good but unless designed right will not function to full efficiency. Any idea why they didn't do a 4" or similar?