I hope I can pick your brains here. My parents have an '07 F150 with the 5.4L. Apparently they were driving it one day and the temp garage rose drastically and was maxed out by the time they got home. Very Short trip and limped it home when the temps were getting high.
When they got home they let it cool down and checked the coolant levels. Empty. No white smoke from exhaust or loud bangs when they were driving it last. Still fires up and runs fine for the very short period of time I tried it. Here's the thing, when we attempt to add coolant to the system, it drains straight into the oil pan quickly. Not over night, but within a minute.
Once it was cooled off, we drained the oil and it wasn't cloudy/milky. But rather antifreeze and oil separated. The dipstick oil had antifreeze and oil on it but was way over the full mark.
With it getting hot I hope it didn't warp the head, but I don't think they drove it long enough for that to happen. Naturally when there's coolant in the oil you think a head gasket or intake gasket but like I said earlier, there was no white smoke coming from the exhaust when the problem originally occurred and the coolant drains so quickly I want to think it's something else. I don't think it's a hole in the block or anything as it runs fine still and they did t hear anything loud pops or bangs when the temps started rising.
Try an engine stethoscope. Drain the oil and put a large pan underneath the truck at the oil drain. Pour water (it's cheaper than antifreeze) into the radiator and start listening to different parts of the engine and see if you can hear where it is leaking into the oil. If you can pinpoint a spot then that's at least a starting point to figure out if it's a head or a cracked water jacket ect... Hope this helps because I would really like to know what it is.
Sounds like what happened to my '65 GTO when the timing chain cover which also served as the rear wall of the water pump developed a hole from erosion or something. This was back in the '70s, I wanted to cruise ..... three times one night I had it on a lift, let set a little bit, opened oil drain and drain coolant out, put plug back in, top off coolant, cruise more.
I replaced the timing chain cover (a cast aluminum piece) and a few weeks later .... had to do it to my GF's GTO.