Greetings all. New member, I joined looking for some help on an issue with my 2013 Suburban. It has 82k miles. This summer it started giving me the P3400 code multiple times. There’s is now a noticeable hesitation/vibration when the truck goes between V4 to V8 mode. I cleared the code a few weeks ago and got an appointment at the local Chevy dealership. They tell me there is no issues, no codes, and the truck seems perfect?? So they can’t fix anything since they don’t think it’s broken and now they charge me hundreds of $ to “diagnose” nothing.

My powertrain warranty runs out in a month and I really hope to get this figured out before it expires.

Has anybody had issues like this?

Thanks!