Do you have another tech2 to try?
From what I hear/read, most poor quality def problems are a bad NOx sensor ( ECM doesn't think def is changing NOx enough). I assume the ECM has all the latest updates?
One other thought.... Is there any evidence that a mouse has chewed on any of the wiring in the truck. It has been cold enough that a mouse may find the engine compartment nice and warm.
Fwiw... I'm sitting at my desk at work just across 35w from Rosedale chev (cty c & fairview)
Jay
2023 Tahoe 3.0l diesel
2013 Harley Switchback
2021 Ram 2500 6.7l (sold)
2018 Chevy Traverse (sold)
2021 Silverado 3.0l LM2 (sold)
2019 GMC Sierra 6.2l (sold)
2019 Colorado ZR2(sold)
2017 2500HD CC D/A (sold)
2015 1500 CC High Country 6.2l (sold)
2010 Chev 2500HD CC D/A (sold)
2013 Chev 2500HD CC D/A (sold)
2006 Chev 3500 CC D/A (sold)
2005 Harley Ultra Classic (sold)