7.3 Broken rings cyl 1 and 3 Again?
 

Guys I am looking for a common denominator on why the compression rings would fail under 100K miles. Here are the details.

stock 2000 7.3 f350 service trucks. lightly loaded. In the the environment of Mali Africa. Hot and dry. Fuel is filtered through stock setup to a added screw on style. (double filtered). Has the big factory M1 abrams Air filter. Trucks are manual trans with the same driver.

Incident happened both times on moderate driving at 50MPH at least 4hours into a trip. no noise then all of a sudden knocking noise as if it it where a rod bearing or lifter. increases with rpm. Shut down the engine looking for a cause let it cool Finding nothing. Fire it back up noise is still there but keep going as there is no smoke and no friendly's for hours. Strangely the noise slowly goes away as we continue to drive until completely gone. Never a loss of power during all this and oil consumption is the same but a puff on startup. Hundreds of miles later we pull things apart looking for a cause. Turbo is perfect hot and cold side. Nothing in the oil pan. heads off no valve damage. Nicks in the head and scoring on the cylinder 1 & 3.
Most of the upper compression ring was intact say 3/4. The lower ring was even less damaged. The pistons beat the rings to a pulp and spit them out with out any valve damage. We put new pistons rings and bearings in it and new valve seals with nothing else new even the same injectors and continued to drive it for 3 years no issues. That truck is now gone.

Carbon copy that story to the point of the noise went away on the second truck that just happened recently it has 53K miles on it. It now starts up with a puff of oil smoke but clears up quickly.

Can anyone tell us what might be causing this?