C-15 Acert blowing oil

"under the truck was covered in oil like someone sprayed it down" explain under, you mean the oil pan and lower than that? What about from the valve covers on down?
"All along the oil pan gasket seems to be really wet with oil all around both sides." When there is an oil leak above the pan (not the pan gasket leaking) oil will collect around the pan gasket. Does not necessarily mean the pan gasket is leaking.
Best thing to do is clean the engine really good with degreaser and a pressure washer. Then get it hot, run at high idle and check for leaks. If nothing, drive and recheck.
Have someone run the engine up to 1200 - 1500 rpm and see/feel what is coming out of the breather. A shop can check the blow by pressure which is quick and easy and should not be expensive.

 

Is it possible you have a rubber plug go bad that sets in lower part of block? There is 2 per side but one hole is used as your dipstick tube.

 

Drop the pan and replace them all. They get hard as a rock and crack apart. Where 1 fails the others are right behind.

I call them spool plugs. They look like a spool of thread.