You might want to have a leakdown test performed on it. Had no outward evidence of a bad head gasket on my '80 20R, but when compression was applied to #1 cylinder, bubbles came up through the intake manifold's choke hose <img src="/forums/images/graemlins/angry.gif" alt="" />! Your symptoms sound very similar to mine.
Good luck.


'80 4X4 Longbed