Steering's gotten stiffer...

Ok, when I first noticed this, I checked my p/s fluid. It was somewhat
low, so I bought some DexronIII ATF from CT (Mr. Transmission brand)
and filled it up, so it was between the hot-cold line, as shown in the FSM.

But the steering still feels a little stiffer. It could be the cold weather, but
could it be something else I can look into?

The rest of my car seems just fine, no problems anywhere else with
steering or anything.

Thanks,

Perhaps your ps pump is getting worn a bit, or perhaps on its way out.

Did you check your rack for leaks?