Interesting info so far. Questions that I would ask:

On the 5.9 that has gone thru 4 sets of heads?
were these new heads or purchased from a recycler or private party who took them off to upgrade or maybe had cracks?

Other question would be, does the problem seem to occur with high mileage?

And were the engines run for awhile with MIL light for say vacuum leaks or misfiring cylinders?

Some of the statements seem to indicate my earlier opinion that engines may have been run with the engine having preliminary problems.

Appreciate the info and would still like specifics on what engine size, year and what the history of the engine is; did you have it since new etc? have a great weekend.

doc