2017 Kensworth T680 ISX15 Automatic Turbo/RPM issues

Hello, I’m having an issue with my 2017 Kensworth T680 ISX15 with an automatic transmission. When the truck slows down and does a downshift , the RPM’s get stuck low and the turbo accelerates a lot but the RPM’s remain low and get stuck there for a second until it does the next downshift and keeps doing until it comes to a stop. When accelerating, no issues shifting except you can’t hear the turbo. But when it’s downshifting the turbo accelerates high with each downshift. It just started doing it this morning. And on top of all this, no check engine lights whatsoever. I had a mechanic look into the computer and shows no codes, checked the actuator and turbo and no issues. I’m at a lost. Thank you in advance.