GG, here's what I would do.

Run the engine to operating temperature and drain the oil and replace the filter.

Remove the oil pan and clean out any sludge you find there and reinstall it.

Then use HRL's engine flushing method to remove all the crud.

Refill the crankase with the cheapest oil you can buy and fill the oil filter canister as well. Add 2 quarts of diesel fuel to the crankase.

Start the engine and run it for 30 minutes at 1500-2000 rpm. Do not drive the truck - just let it sit there.

Drain the oil and diesel mix and replace the oil filter.

Fill with the quality oil you normally run in your truck. It will either smoke or not. After this you can decide whether to pull the head and make repairs to the valve guides

1950 Chevrolet 3100 (Ol' Roy)

1939 Packard Standard Eight Coupe (The Phantom) | 1956 Cadillac Coupe de Ville (The Bismarck) | 1964 Ford Galaxie 500 coupe |1966 Ford Mustang (Little Red) | 1969 Pontiac GTO (The Dishpit) I 1979 Ford F-100 | 1976 Ford F-150 (Big Red) | 1995 Ford F-150 (Newt)