engine trouble, oil pressure diving

30 - 35k? Here is what I would check first. Thrust bearing, Pull the damper front and then push it back, See what play you have in the crank thrust bearing. A tight converter with a larger cam will wear the thrust bearing,

Check the lift on the cam at the rockers for worn cam lobes. Could be a hole in lifter. an engine with 35k that developes and issue would more then likely be a worn part.

A cheap filter would also contribute to pressure drop due to bad construction of the drain back valve Fram and STP are noted for this, I use only NAPA Gold or WIX. Nothing else