If you've got the tools, it wouldn't be a bad idea to find a scrap motor and start rebuilding it in your garage. You can pick up a non-running motor for dirt cheap (make sure you have a good idea of what's wrong) and rebuild it in your spare time. If this motor goes soon you'll be ready to go, if it's fine you can sell for a decent profit.

 

I just recently had this exact thing happen to me 2 days ago. Cruising 80 down 412 in Oklahoma and boom check gauges light and truck dings. No oil pressure at all. I **** it down and check oil to find it full. Truck has been making a noise sounds like an exhaust leak.. or maybe a slight normal tick at times when up to speed and temperature. Never had any issue with pressure fluctuating or any notice of an issue. Not sure if it relates to you but I ain't switching motors in a 2003 with a gas hog hemi lol. Might as well get that cummins 😁 but I do think it's the switch on mine and gonna start there

 

Pretty common to lose the sending unit(switch) on these trucks.

 

I had similar issue....two weeks ago going to my shop I was slowing down, check gauges came on and my oil psi was very low (pulling in it’s a downgrade, when I leveled off in parking lot psi went back to 40....drained oil and maybe 2 quarts came out (after 3500 miles. I run Mobil 1 10w30 synthetic)

i knew my rear main was bad so ordered new one, plenum leaking, ordered Hughes plenum kit, oil sending unit leaking so I put some thread tape on, got valve cover gaskets, oil pan gasket, crank seal, timing gasket set with double roller chain...all these are leaking so I’m replacing everything. Got my parts just need to finally do it.

the combination of all said above contributes to some pretty good oil loss. All above parts plus more only cost me just under $300