You mentioned a adjustment to the brake rod.. is this the one from the pedal to the booster? Or the one in the booster to the master?

Another thing a lot of folks have trouble with is some of the older bulkhead fittings, they pass through the frame rail, to join the line on the inside (or the inner side) to the outer line or hose. there were some made some years back that had a larger I.D. that will actually capture air and will be near impossible to remove. Perhaps you can remove a line and see if there is a larger I.D. that could capture air.

Another thought is if you have a power bleeder, go backwards, that is, push fluid from the caliper, slowly to the master.