Slipping transmission
 

2014 Silverado crew 5.3 6L80e

Truck has been clunking with downshifting for a while, mostly 3-2 but some in other gears as well. It just started doing this however in the past 2 days. Powertrain warranty is still good until 10/19. I wasn’t sure if I was dealing with a Ujoint or transmission issue until this started happening. It certainly looks like a slipping transmission to my untrained eye. Truck was bought second hand but appears to have had an easy life. To my knowledge the transmission has never been serviced, however manual doesn’t recommend until 97K. I checked fluid levels and it was within the marks and as you can see the temp is within reason. Looking for input from the forum experts so I can do more homework before taking it to GM garage this week. Thanks.

Clarification
 

The clunking has been going on for 6 or more months, however the slip that is observed in the video has just started happening.
Sorry for the confusion. Thanks.

Clunking could be u-joints but either way get it inspected.
I would take the truck into the dealer. They should be able to read live data & possibly the clutch volume index CVI and also scan for any stored transmission codes etc.

I agree, if its still under warranty, get it to the dealer ASAP.

Update
 

Took my truck to the dealer for Repair. They say it’s most likely a bad torque converter and is still covered under the Powertrain warranty. They also said there could be more damage once they get a look at it. Thanks for the replies.