Milky oil means you're getting water and or gasoline in it(quick smell will verify antifreeze or gasoline).   Oh - water builds pressure nicely in all the wrong places, especially if it's turning into steam inside the block's various internal passages.

Gasoline smell means it's above the cylinders/the head and the gas/water combination is draining slowly into the lower block past the rings.  110% bad gasket in that case.   And, will likely eat the old gaskets out in short order - compressed steam , even a small amount of it is a fantastic solvent.  The first time this happened to me a few years ago, it went from "I think I have a problem" to dead engine in about a week. 

If it's just watery, then it's not *quite* as bad(still, something's blown or sure with your truck)

P.S. I'd get working on this asap - and check to see if the cylinders are wet/have water in them, because sitting water in the cylinders can cause a world of ills quickly.

P.P.S. Don't run it.  When it goes dry, you'll have 0 viscosity oil(guess where the water went) and the temps will also skyrocket and warp the head for sure.