Heath,
I have not read everything on the thread closely, so forgive me if this has already been suggested.
Coolant puke; some causes are: missing thermostat, thermostat stuck open (just like missing), bad radiator cap (not all of them are made to have coolant flow both directions), bad fan clutch (not locking up when hot).
"Missing" condition when warm. I noticed this on my old truck when the oil was very low. Presuming your oil is up to the correct level, it is possible that the oil pump is worn enough to lose effective pumping capacity when the engine and oil are hot. Oil will not fill the lifters enough, causing missing sounds because the valves are not opening. Since the pumps are meant to produce volume and not pressure, if they lose their ability to pump lots, they cannot make it up with pressure.
I will not suggest that you jack up the radiator cap far enough to drive a new truck under it, but hope you find the problem soon. This kind of issue, while not necessarily dangerous to the engine or driving, is extremely annoying and (good news here) usually inexpensive to repair, once it is diagnosed.
Good luck!