Shifting on interstate

[Daniel Johnsey]

I have a 2015 Chevy Silverado 1500. Yesterday driving down the interstate with cruise control on I noticed the truck shifting back and forth between fourth and fifth gear. It seemed to hold fine when I would take the cruise off and hold the speed myself. It would also stop when pulling a hill as it would stay in fourth gear. Today it seemed to be doing the same thing in the lower gears and the check engine light came on as well. Planning on hooking it up to the scanner tomorrow but am looking for any ideas of where to start. 

[CamGTP]

It should be cruising in 6th gear and not 5th unless it didn't have 6th gear or it was locked out of it with the shifter in Manual mode. But the up and downshifting with cruise control could be "normal" depending on the road. If it has hills the truck will downshift more than if you were just using your foot to control speed.

 

Hard to say what the issue is without knowing what possible codes it's throwing.

[KLRV6]

Probably the torque converter failing and can't stay locked in 6th. If you haven't tuned the trans or replaced with a full billet convert, a rebuilt is in the near future. Drop the pan and check for metal or clutch material.