The third finger has much more strength when the little finger moves with it. This is harder in my left hand, since I have a ligament separation between the fingers and they don’t naturally move together like the do for most people (like the trick where you lower the little finger and the third involuntarily lowers itself too). I have to consciously move it. To help, I try to pretend they’re one big finger when I play.

I also have some issues with reaching certain intervals with the third finger, particularly a fourth (don’t even ask me to play an unbroken fifth!). I’m a but envious of some harpists who seem to have these superhumanly long third fingers. Mine isn’t terribly short, but compared to my fairly long first and second fingers it is. And because of the relative length of my other fingers, sometimes my second finger has to bend quite a bit to fit into a chord while the third is much straighter. It is tricky getting the same tone out of both fingers sometimes, like a 4 note chord with the dominant on the bottom.