Posting here too...
Hey I have a 2019 Bighorn 5.7 that has done this since I drove it off the lot. Took it to dealer 3 times, last time they replaced the ECU. After a drive cycle, misfires come back in Mode6 data. Short term fuel trims while idle are -15 on bank 2 and -10 on bank 1. When crusing and driving normal, its as close to zero as can be. I have no idea why the ECU thinks it needs to run lean like this at idle. Only thing that helped was disconnecting both upstream O2 sensors, ECU runs open loop and idle is fine. Reconnect and it went away until a drive cycle or two, mode6 misfires show and Short Term Fuel Trim back to -15 on bank2. There has to be a PCM update that can help with this, its really annoying. I get the HEMI is a big V8 and can shake, this is like bucking and missing. Anyone get any progress with a service dept or STAR case?