2018 freightliner dd13 def issues

Hey guys im new to Trucker report and i had a question concerning one of our freightliners. it's a 2018 dd13 Cascadia. its throwing the code for catalyst at high limit for the scr. at first while running a regen I noticed the outlet nox sensor reading wasn't plausible so i replaced it along with the inlet. it still will not raise the conversion efficacy and seems like to me the def pump isn't dosing during a regen or parked scr efficiency test. ive removed it and done a quantity test and it passes. swapped the doser with another truck and still doing the same thing. so far been doing another scr efficiency test and the inlet nox is hovering around 500ppm while the outlet is 600ppm. dealer is saying maybe a new one box but i don't think that's the issue any help would be apricated thank you. 2018 freightliner Cascadia dd13 last six of vin are JN2520