Trying to make my attic air conditioner more efficeint

da_man

I just moved into a house the beginning of the year. I have two furnaces, one in the attic and one in the basement. My air conditioner in the attic noticeably has warmer air than the air coming from the one in the basement. They are both cooling the air in the house, but the one in the basement does a better job. The temperature in my attic is getting up to 125 degrees on 90 degree days. Some things I noticed are

the trunks and lines are insulated with what looks like r3 or 6 . Can I go to a higher R-value? if so where do I get it?

The air filter is 24x16x1 and the media air cleaner is not sealed. there seems to be a 1/2 inch gap for the filter opening. Can I get a sealed unit and have it insulated. If so where would I get it? Also where would I get a sealed unit.

Also would there be anything else to do? like should I worry about the registers, connections, tape joints, or anything else.