Steering issues

I have a 2008 Tacoma TRD sport, 4WD, king cab, extended box. Approx 160,000 kms on it. We have noticed lately that the steering has become harder, as if the power steering fluid had leaked, but the fluid levels are fine. It also makes a squeaking noise when turning the wheel, especially after it has been sitting for a while. The truck is used daily. Any thoughts on what could be causing this. We are wondering if there are other mechanisms that wear or that need lubricating. We also had Goodyear Wrangler tires installed for the first time, and we have inflated these to approx 38 psi. Tires are rated up to 45, but we found at 38 it gave us a smoother ride. We had a little vibration, had them balanced again and found that the higher psi helped. These are new tires.
Anyone else have experience with this.
tks
Lesley