QSX15 hard start/extended crank times w/black smoke

[dodges15152023]

Update on tractor, we finally resumed troubleshooting this unit, the engine passed the injection pressure test, running them through process multiple times to assure accurate results, interestingly is how well it held pressures.
Ultimately the engine lost all of it's valve lash on the exhaust, at minus lash it was holding the exhaust valves open, the intakes where at .005/.007
All valve settings albeit tight where identical, so whatever was wearing was equal.
I reset all the valves and the Engine starts and runs excellent.
The tune had already been updated prior to running overhead.
So did the old tune degrade the seats and/or valves?
Do we pull the head to be on safer side and inspect?
1700 hours on engine.