C13 - getting hot cracking heads

Alright, one of our C13’s a LEE prefix is having major issues. It all started a year ago when the low pressure turbo started to fail. I called cat and it was 45-90 days out on back order. I got 2 from highway and heavy parts, 1 didn’t fit right, the other lasted 2 weeks. There’s a performance shop near me that has a good reputation around here. I called him, he suggested throwing a single conversion kit on and tuning it for a single. Sounds good as my other option was to let it sit for 2 months…and milk goes bad in 2 days, so it was a simple answer. About a month after installing the single and running this truck, driver called that the coolant tank is empty and dumping air. Diagnosed, head is spider cracked all around #3 piston. Ok, cat is also back ordered on this head. Got one from ATL. I #### you not, the ATL head survived 3200 miles before the valve guides ground off. Got the ring around and shafted from them. Ordered ANOTHER head from highway and heavy, with oconell valves. This one lasted 15k miles before spider cracking on 1 and 3 piston locations. I finally took it to the guy who installed the turbo kit and delete tune and said since you’ve tuned it’s been junk. He opened up, checked deck heights just as we did, they are low, but still in cat spec. He found a new cat head, and installed. For the first 15k miles the truck egt temp never got above 650, now today I had couldn’t keep it under 950, so it’s doing it again. What the heck is causing this? Faulty tunes? Low deck height creating heat and head gasket displacement? There’s 1 code that’s always been intermittent since delete tube was installed, and that’s engine air intake sensor. Could we be dumping hot air in causing high temps on #3? Charge cooler is not leaking. The single kit is a borg Werner, direct replacement for a c12. It runs about 26-31 boost. Manifold is full tilt performance. Other than that, sleeves and pistons are in perfect shape. Any ideas? I’m ready to dump it off at an auction but i couldn’t do that to someone else. It does seem to have an enormous amount of power. BUT my other c13 that is stock rated at 475 is neck and neck with this truck.