I'd 3bet a lot of good nut AAxx hands, and one's with good side cards, otherwise I'm just flatting and top-set mining
OOP I'm 3betting even less
There is a rule of thumb, try to get XY% of your stack in PF, and if you cannot, don't 3bet/4bet AAxx. I'm not a huge fan of this thinking, but it's probably not a bad idea to start with.
One thing to look at is how you can use short-stacks to your advantage to get a lot of money in PF, don't always pot-3bet/4bet AAxx because you can force the action to be closed if a SS jams behind you, try and make your raise size small enough so the action is re-opened should a shorter stack jam. This isn't as rare of a situation as you'd think and I see people misplay it frequently here.