Hi volume oil pump

At idle my rebuilt 360 gets about 22psi and at 60mph (2200rpm) I get about 60psi. I have a mechanical autometer guage, stock pan,stock pick up tube, with a hi volume pump, 10w30, and a short Wix filter. I did drill 4 extra holes in the plate under the filter and I pollished the rocker arms.
The only time I have ever had oil pressure as low as your motor was with the old 360 that was in my car. At idle it would be 8psi and at 2200rpm it would be at 17 psi. No knocking or anything, I just pulled it apart this last weekend (after sitting for a year and half) and all the main berrings were shot to hell.