2012 Silverado 160k miles 6l 80 trans
when shifting from 4th gear to 5th, trans will shift back down immediately and then back into fifth. Shifts a bit hard when doing this. There's also a whirring or spinning noise during this. almost turbo like sound that occurs too, but more of a tornado siren type noise. Seems to not occur or very subtle when cold. When warmed up noticeable.

​​​​​​Fluid smelled bad but was correct level. Draining, replaced filter, filled back up. Slightly better but still there.

 

The tcm's (transmission control module's) are prone to fail in these. Not keeping up with the oil changes don't help either. I installed a rebuilt 6l80 in a 09 escalade and first drive it shifted hard, flared neutral and never threw a code. I replaced and had the tcm programmed by the dealer. That was 20k miles ago and still no issues. The tcm is bolted to the valve body. The valve body needs to be removed to install/remove the tcm. Did you have a ton of clutch dust and/or metal parts in the pan when you changed the fluid?

 

Didn't appear to be much metal or dust. Some build up on magnet. Nothing notable though. Does the tcm need to be reprogrammed if it's from the same gen/truck/trans?

 

Sounds like all your hard parts are still in good shape. I've only replaced with new units that required needing being programmed by the dealer because one of the tcm failure symptoms is burning up the transmission by blocking off fluid flow to certain areas. If you do get a used unit make sure it is within a couple years of your truck. The operating system is a little different in certain years and can cause all kinds of shifting problems without the proper reprogram.