So I've got a buddy who has a 2014 silverado with a 6l80 transmission, completely stock truck. The truck will not shift on its own. He can manually shift the truck all day and it works perfectly fine, no slippage or anything. What could be the cause of this automatic transmission not automatically shifting

 

Nobody?

 

Any codes set? Speedometer work? More info would help.

 

Probably a hydraulic leak somewhere on the valve body and/or valves.

 

I'll ask him what's the codes, and the speedometer works just fine. He just has to manually shift