stoveboltgunnut
+1y
I realize I'm new here, but I'll say my piece. You need to do some diagnostics. Blue smoke is oil burning. If your valve seals were bad, it would smoke more when you let off of the accelerator (the engine vacuum pulls oil past the seals and into the combustion chamber).
You need to do a compression check. Dry first. Write down the numbers. Then use an oil bottle to squirt two or three shots of oil into each spark plug hole and re-do the compression test. If the numbers go up dramatically, your rings are stuck or worn (the oil that you put in the cylinders helps the rings seal a little better and raises the compression.) If the numbers do not raise with the oil, then you probably have a valve problem, a cracked head, bad head gasket, etc.
If you have low compression on two adjacent cylinders (1 and 2 or 2 and 3, etc.), you probably have a bad head gasket or a cracked head or block.
The compression test may not pinpoint your exact problem, but it can certainly narrow it down. Point is, I highly recommend that you run a compression check before you sell the truck or tear it down. It could be as simple as a pcv valve too.