I need Ideas on what to check.

[Bamaprez]

My Motor is a demandated CPL 3606 set to factory 550 1850 tq. 750,000 heavy haul miles. in a 4 Axle VNL 18 speed 3.90 gears. Max boast 32 LBS Max EGT 930 post turbo. Now for the issue. started losing water last fall. Took into my Shop. "reputable has done a lot of work for me over the years. Trouble shot down to exhaust in radiator, pulled head found cracked head between 4 and 5. Decided to do in-frame while we're there because of millage. All cummings parts "That took a while". After inframe truck made 250 unloaded mills before #5 liner split and got the piston, No rod damage or crank damage found reluctor ring chipped. Pulled motor back down checked crank, shop checked and measured block where liners insert and recut counter bores pulled orings and installed liners and measured protrusion. I was there to witness this. after second infram I drove truck approximately 500 unloaded miles then decided it would be ok to load it. After 328 loaded miles babying the truck. KaBoom Haven't pulled it down yet but sounded like the same bottom end let got. Will start tearing down with my mechanic Monday. I'm sick and at a loss. I might could understand it the problem started with a bottom end issue but that did occur until after the first infram But it started with a cracked head. any direction to look would be appreciated. John