At this point i would just add that datalogging inside attic temps vs outside air temps would be a good way to go. Also if your ducts are close to the bottom of your floor in your attic just bury them with a bunch of insulation so the large temp difference in summer doesn't hardly make a difference as it really doesn't make it to the ducts. If you can bury your ducts in insulation and seal your celing and wall penetrations with expanding foam you should be as efficient as the new houses that are spray foaming their roofs but you don't have to air conditon your attic and you can work with what you've got.
Also, soffit baffles. You can just use cardboard and it helps you go edge to edge with insulation if you have loose fill. A lot of the time with loose fill houses they don't do much on the outer 1ft so it doesn't blow into the soffit baffles so essentially the top part of most of your outer walls aren't hardly insulated.
*Also, seal your ducts with mastic. We don't want any sucking or blowing from the attic into your ducts or house.
Coolcalc isn't that accurate for high performance but its helpful.
https://www.coolcalc.com/
Run this on your house boys and see where you're losing your energy. the report will tell you losses from ducts, windows, ceilings etc.