Josh04f150

I have a 2004 f150 4x4 5.4 liter and if I Drive it on the highway for about 20 minutes or more and get on it I start losing oil pressure in the engine starts knocking I can park it overnight and it will run fine for a few minutes then it'll start knocking and losing oil pressure again after a couple days it'll start running good until I Drive it on the freeway again then it repeats the process of losing oil pressure and knockingwhat could my problem be