Only use the Ford/Racor filters. Also I would even try a third guage on it, because if the low pressure system is not up I see no way the high pressure system could keep up. But I would first eliminate the filter problem. Wrong filter may open the bypass/drain in the housing.

 

We're going to have to assume that there is oil coming from the lpop and making it to the hpop since the truck is running, and you're seeing pressure at a higher RPM. In order to have pressure there has to be a restriction somewhere. So some obvious places to look have already been mentioned. As was mentioned earlier on, the drain back valve in the oil filter canister, the plug in the HPOP both could reduce the restriction thereby lowering the oil pressure. Just me guessing here.