Mine maintains 75 while set at 72 during peak 106+ days lol
it is what it is

82 though is not acceptable

mine is 10 years old, 2 units

Humidity levels? Sounds like maybe air infiltration from the attic

We live in an 84 yr old pier-and-beam home near The Heights that has horrible insulation and aging HVAC. AC seems to be struggling worse this year than previous. When we moved in, I bought an LG 15000 BTU/110V window unit for the master bedroom (East side of house) to supplement, and in case the main AC or power went out (it will run off our generator). Judge all you want, but I can get the master bedroom to 63 degrees at night and sleep like a baby! This year we've been leaving it on low during the day and place a tower fan in the doorway that blows the cold air into the hallway/other rooms. Helps take a load off the main one.

Then on Prime day this year, I came across a Midea unit on sale that had great reviews and bought one. It's a "Smart Inverter" unit (the fan speeds up/down as needed to maintain temp) that is "U-Shaped" with a split down the center that allows you to almost completely close the window (pic below). This cuts way down on the noise (we can barely notice when its running on high). I put this one in the living room (West side of house) that struggled to get below 78 during the day. I keep it set at 73 during the day when we are gone to work for the doggos.

I now set the central AC to 76 during the day and it rarely kicks on. Once I get home, I set both to 70 until dark then switch on the central AC. Def worth it for us since we dont plan to be in this house much longer and dont want to spend money on new insulation or a new HVAC system. And both units are on the east/west walls of the house, hidden behind the privacy fence so no one can see/hear them. I'd recommend picking up one of these to supplement your current system if you don't want to drop thousands on a new system or insulation.

https://a.co/d/dJHNQjV

We have a variable speed Lennox in the house & it has handled this heat just fine. No matter what we set it on, the dehumidifier function keeps it about 3 degrees under that.

That said, it's just the 2 of us & we have always had a window unit in the master. No one can see it and it's like a meat locker in there at night!

edit to add: During our recent renovation we went overboard with insulation in the attic to compensate for lousy windows - 1960's single pane crank out metal casement windows that LOOK fantastic but let in plenty of air. I think we could BBQ in here & not have a carbon monoxide problem.