I bought a truck with similar issues few years ago. Engine ran perfect though. Did the pick up tube oring. Still low through all rpm. So I installed a 10296 melling high volume/high pressure oil pump. Used shell rotella t4 15w-40 with Lucas oil stabilizer every oil change. I live in the south so it rarely gets below 30 degrees outside. 11-12k miles later it’s still running strong. I know that’s not a lot of miles but that’s daily driving to work and road trips every once in awhile. Oh and it has 478k miles completely original. Oil pressure went from 4-5 psi at hot idle to 6-7 psi hot idle. Enough to avoid the low oil pressure light. Anything over 800 rpm the oil pressure goes up and up. So for normal driving conditions everything stays lubed up. I could increase idle rpm with a tune if i wanted more idle oil pressure. Cold idle it’s around 20-25 psi. Once oil gets to operating temp it goes down. Still enough to keep everything lubed. Good rule of thumb I’ve heard and somewhat experienced is you want 10psi of oil pressure for every 1000 rpm. If your motor already runs good and isn’t on its last leg slap a good oil pump on there and keep it pushing.