Oil pressure Question: What causes this?

Have u ever looked at the size if the ports in all the fittings u are using? It just looks like the lines may be a little restictive. Rule of thumb would be the more length-bends-fittings= need for bigger lines. Also the finer the filter the more pressure drop at the filter. With all the lines you show in the pic's I would be using at least 5/8" id lines then your restriction would be right at the block and no where else.