For what it's worth that's pretty much where the pressure is at cold idle and warm operating speed with my 5.2.

 

If you changed it cold the oil in the filter probably just drained out. The filter they use doesnt have an antidrainback valve. Thats nothing to be worried about. The new oil isnt broken down like the old oil, which will make the pressure higher. I used 20/50 in my 4.7, didnt hurt anything, just wasnt as good on gas, which is why they use thin oils. I use 15/40 or 20/50 in all my vehicles in the summer, lighter oil in the winters. If youre reading good oil pressure your pump is good and the bearings arent worn. o be sure, get a mechanical gauge and check the pressures hot and at all rpm. For every 1000 rpm there should be 10 psi, so at 2000 it should be around 20, etc..