I remembered another thing. EASY fix. If, at sometime in the life of your truck, it was filled with plain 'ol water, well that caused rust, cavitation, etc. The soft plugs can be damaged when just water is used. When you drain the water and install coolant, the damage should stop, or be slowed from progressing further. Well, if this has happened, there are a few soft/freeze plugs in the head, under the V/C that will leak, causing coolant in the oil. Most of the time when the start, they leak under pressure only but get to the point that they leak as fs as coolant can be putin. When you pressure it, remove the V/C to have a look at these. If they are the leakers, just do them all and you'll be done.
Just a thought
