I have an AC that works great when it's under 94 outside, but anything above and the temp slowly rises in the house, then takes a long time to get out, usually until 11pm at night, sometimes all the way until 3 in the morning. I plan on adding some insulation to the house, as I just had the coils cleaned and I would like to hopefully not have to buy a new AC unit. Where I live in Texas we have been experiencing pretty hot weather, 100-105 for most days the past month and half-ish. When I go into the attic and touch the main ductboard trunk line, I feel that it's pretty cool to the touch and can tell that AC is in it. Can/Should I use any of the duct insulation @ home depot/lowes? From what I've read online it says that ductboard doesn't need insulation, as it's inside of it. This weekend we plan on adding 6 more inches of cellulose blown insulation to bring it up to 12", installing solar window screens on the W/SW side of the house, and probably adding an attic fan. Should I worry about further insulating the ductboard? Does anyone think this will be enough? Any alternative suggestions?

Ductboard is already insulateed... there is the chance that the insulation in the board might have fallen down. Does the box feel week on top or stiff?
Personally I would not wrap or do anything to it. Do the other things on your list first.