If you're running the original-style external filter with the cartridge insert and the screw-on top, it will have a 1/16" diameter flow restrictor built into the standpipe the filter cartridge slides over. If someone has plumbed in an add-on filter adapter with a screw-on canister, most of the oil flow is probably returning to the crankcase and very little flow is getting to the engine without a restrictor installed. This will also drop the oil pressure to dangerous levels.

The pressures you're describing are normal for a full-pressure 235, and a cooler isn't likely to improve it much, if any. Any oil pressure at all indicates that the pump is delivering more oil to the bearings than they can leak away- - - -even one pound of pressure is an indication that the engine is getting all the lubrication it needs, plus a little more to make the pressure rise. If the oil was leaking away from the bearings at the same volume the pump supplies it, the pressure would be zero. Thicker oil such as straight 30 weight or heavier will increase the pressure, but there might be concerns about getting the oil to go everywhere it needs to on a cold start. The only way to get an increase in pressure will be to flow more oil volume to the bearings, and I don't think a high-volume pump is readily available for the 235 engine. It might be possible to adapt a pump made for a GMC engine like a 270 or 302- - - -not sure if that will improve things or not.
Jerry

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