what kind of oil

hi just looking to see what kind of engine oil u guys run. i run shell 15w-40 rotella in my 416 stroker. the previous owner ran nappa 10w-50 raceing oil but i cant seem to get it here. nappa tells me there is no such thing but i know know there. is my oil pressure is sbout 5 psi lower with the 15w-40.i use shell rotella in my boat a671 detroit with 22 thousand hours on it only ever replaced 2 goveners so it must be fairley good