When you check the cabin filter, make sure the cover is properly seated on the housing when you return it. Take the opportunity to replace the foam gasket with a polyurethane insulator. When the insulator is bad, some air leaks causing the CFM drop.
If your motor and filter housing is missing the foam insulation that covers the entire unit, you should buy a replacement for it. If not, hot engine heat can reduce the efficiency of the AC.
I actually had CFM and cooling issues with my unit. I had checked out temperatures, freon pressures and performance to make sure everything is ok. But I wasn't pleased with the CFM and cooling. After I replaced the gasket, I also fabricated 2 layers of reflectix insulation over the housing and put the OE foam insulation over that. It made quite a difference!