That seems a little low, but understand, I don't have what I'd call a ton of experience with Magnums. I've built several, but for other people. I always use high volume oil pumps.
Yeah, slants usually have a lot of oil pressure when done right. Mine idles at 75 cold and the only reason it's not higher is because the relief valve is open. When it's hot, it idles around 45-50. As soon as you blip the throttle at all, it zooms up to about 75 and stops like a rock right there, because the relief valve opens. Otherwise, it'd run right on up to 100...or whatever. lol I don't run a high volume pump in a slant, just a standard volume pump with the high pressure spring.
I wonder if the high pressure spring might help with your issue. Not as easy to get to as the slant, but it might be worth a try if you decide to do something.