Have Ford Questions? Ask a Mechanic for Answers ASAP
What happens is the timing chain guides start to fall apart and pieces of plastic start to clog up the oil pick up tube.When the engine is turned off some of the plastic fall back down from the screen on the pick up tube and allow normal oil flow until the screen clogs again.Also if that is not the problem it could be a bad oil pump, because when you first start the engine the oil is cold so the oil is thicker as it heats up it thins out and this decreases the oil pressure.
You can remove it and clean it.You will also need to replace the timing chain guides if that is the case.You need to remove the oil pan to clean it.What size engine does the truck have?
To remove the oil pan the engine has to be raised up.Here is the procedure.