Valvetrain complete, but a few ???'s

The issue isn't the drainback valve in the filter. The filter is mounted completely vertical..it can't drain back.

I AM an Amsoil dealer, and have been using these kits for quite some time with very good results. If someone has issues with it, it wasn't being used properly.

As you can see the filters are mounted verticle. The input line comes from the block, passes through the filters, and on to the B&M cooler mounted at the bottom right of the core support. The return line goes from the cooler back to the block (it is dressed up now, and lies against the inner fender. Just to the right of the pic the line inclines up to keep the oil in the mount, then turns down to the block. the only issue that is present is the 12" or so of line between the block and the curve that can drain back in to the pan. When running I have very good pressure.