Re: Melling vs OEM LPOP
Ah, yes, if you were expecting all of the oil to get to the reservoir through that little port in the front cover, then yes. I can absolutely see why it was dropping pressure. But that would still be rpm related, not throttle related. In that case the lube oil pump capacity was coming up with the volume usage of the high pressure system, it just couldn't all get through the feed port and was going elsewhere instead.
The additional feed line is why the issue was resolved, not the lube oil pump change. I have never run the truck without the additional -6 feeding the reservoir.