CDL Roofer

Good Afternoon, I have a 2017 Mack GU813 roll off.we have a check engine light that keeps coming on. we have had the turbo changed, hoses leaking fixed, and the turbo sensor. the truck runs great. no idle issues, no running issues. it goes when i tell it to and it stops when i want it to. but for some reason, the truck keeps throwing a check engine light. its been back into the dealer 6 times now with no solutions thus far. the light is off for about 2 days or 250 miles or so. then it comes back on. we bring it there. they say they found a small air leak, fix it and clear the code. get the truck back and the same thing happens. can you please give me a hand here? we are trying not to do damage, but we are loosing a lot of work and having jobs stranded. we are trying our best to get it fixed but to no avail. thank you for your inpuit and i look forward to hearing from someone soon.