20 psi seems a little low to me. I'd rather see about 30 at hot idle, but it's still probably okay. The pressure should rise about 10 psi per 1000 rpms when you rev the engine. So, if it does that, it's okay. Gauges can vary, so you could put an inexpensive mechanical gauge on it to see how it compares to your factory gauge reading.
I wouldn't use 20w50 in it, unless you live in a hot climate or it's summertime, because that oil is thick, and even then it isn't necessary. I suggest 10w30 in a cold climate, and 10w40 in a mild climate, although either would be fine in all but very cold weather. And then a 5w30 would be better.
