Engine trouble- Plummeting oil pressure

I am curious what oil your using. Have you changed brand or wheight recently? I've had this experience with a couple of my vehicles. I can not run a partial synthetic at all in my 440. The clearance, I believe in the oil pump, won't even pickup the oil in the pan. My 4.7 05 I can run a synthetic but has to be 10-30 or better. I had a local shop change the oil and put in what the cap says, 5-20 I believe, made it 15 miles in dead cold winter. Stopped at buddies house and pressure dropped immediately. Sometimes motors just don't like syn oils.