the 305 oiling system

[NCali]

87 1/2 ton  305 tbi   75,000 miles on a rebuilt engine
    I drive the truck @ 50 mph or under and the engine is nice and quiet
Over 50 and the rocker arms clatter. I made sure the valves were adjusted properly by (with the engine running)  backing the nut off until the rocker clatters , tightening it until it stops clattering
and giving it 1/4 turn more.  During  the adjustment I saw 1 that wasnt getting oil
Oil pressure @ 25 lbs   The adjustment didnt help, it still clattered after driving on the freeway

I put fresh oil and a new filter, oil pressure goes up to 45 lbs , get on the freeway  and drive @ 70 mph  and it is nice and quiet and oiling like it should

Am I losing flow across a dirty filter

[bd]

How many miles on the oil and filter?  What oil are you using?  What brand of filter?  How did the oil appear when you drained it?  Did you check for fuel contamination?

[NCali]

I had a little over 1000 miles on the oil and filter, I have been using castrol high mileage 10 -40
and a fram filter that time. I put an ac delco on it now

I drained the oil when it was hot so it was pretty thin, After draining the oil out of the filter it felt like it was about 2 to 3 lbs, it was heavy. The oil still had a gold color to it, not totally black
In the drain pan the only metal I found looked like three pieces of wire from the pick up screen
there were no visible signs of metal in the oil
no I didnt check for fuel contamination

[jg1977c20]

sounds like "valve float " as in your valve springs are too weak from mileage to handle higher rpms

[bd]

There may have been some fine debris slightly dislodging the pressure regulator valve in the oil pump.  The lube system has a bypass valve engineered into the filter base that should prevent oil starvation of the engine if the filter is too restricted and when oil viscosity is excessive from low ambient temperature.  The "wire in the pan" is an eyebrow raiser.  At this point just keep an eye on it for recurring symptoms.