Any help would be greatly appreciated

My 2016 Volvo VNL780 with VED13 mother and IShift Trans has started purging air instead of popping off. It purges should 50 psi and everything has been replaced except compressor but no one including Volvo shop, company I'm leased on shop and a shop in MO. can figure it out. I put a used transmission in it and had no problems until the dealer programmed a ecu and it started after that. They've reprogrammed again and a lot of other stuff, but it's still doing it. Not sure if this matters but I have been getting air dryer malfunction on DID almost from day 1. Bought it new and been on computer for several things and no one can explain why it keeps coming up. Any ideas what it could be?