Needing Help ISX CM870 CPL8518

[Bakanka]

15/20k miles ago i have done replacing cams and rocker levers all oem with bottom end as well
When they were putting everything back together they stripped thread on injector side 4 bolts on cylinder 5/6, they did not noticed until i went for a test drive after driving for about 3 miles engine wasn’t working properly like there was a injector problem now they told me you gotta bad injectors. Hooked up to computer and it showed 5-6 injectors. They started disassembling and saw that the new mechanic have stripped them bolds, i was curries now what need a new head? Than i asked him that question, he said no i will fix it with a thread tapping inserts it will work just fine.

After they repaired it i drove it, everything was fine. Went making money with this truck and about 15k miles or little more yesterday it acted up the same way like injectors problem i safely parked at truck stop and opened valve cover and i saw that one bolts head was missing and 3 were loose and spinning in its place no way to tighten them.
I have changed the oil twice after that repair within 15-20 miles.

My question is whats my best option here that shop is taking all responsibility on them but i have to take truck to them. I am in NE have to go to OH. Help is on the way.

On this truck currently over 900k miles and it’s deleted turoos boost doesn’t goes over 38 pyro gauge i see doesn’t goes over 900f it only stared raising to 900 when this problem happed mostly up to 600.