Steering difficult after P/S replacement, low idle

Hello,

I replaced my radiator, water pump, timing belt, and power steering
pump, after I had some overheating from the radiator cracking. The
overheating never got so bad that I heard noise, but I noticed the
temperature gauge was ran up all of the way, and some oil burnt off.

Everything ran fine after the replacement, except for my power steering
started to fade about a month after the replacement. Also my oil
pressure seems a little low when hot, but it is within operating
parameters. The power steering is very difficult at current idle RPM,
about 550, but is easier at higher RPMs. I don't remember the idle
speed or oil pressure before the overheating.

All parts were bought at Toyota dealer, but P/S pump was one of their
remanufactured ones.

So what's do you think is my problem?

Thanks in advance!