new problem losing oil pressure upper rpm's

Kidding aside, I don’t know what your problem is, lots of things to check listed. Heavy oil and drain back is one of interest to me… specifically drain back itself from the heads.

Liquids typically need a vent to drain fast when contained. The none vented valve covers, assuming none vented, seem suspect. That said, simply venting your valve covers ruins PCV function as it won’t draw, or my takeaway anyway.

Solution? - I’m not sure what my success will be but I’m going to do the following.

1. Add hose connections between valve cover and oil fill tube. Specifically I would add a hose barb to each valve cover and two on the fill pipe itself. This would provide filtered vent air to each cover. Plan to add in center of cover, and as high as possible.

2. I’m adding an air/oil separator kit for the PCV system that I’ll drain direct to the fuel pump block off plate.

3. Add drain lines to lower front valve cover and join to drain into fuel pump block off plate.

My plan is to do step 1 and 2 to start, add 3 if drain back seems to be an issue.

Not sure how they are expected to drain once they fill without a top vent? 

Knowing if you have a proper gap, pickup to pan, is something you need to know. Too tight is not good and it could account for what you are experiencing 

Often the reason is...

and the rear of the lifter gallery.

The oil drains back down as demand decreases.