Bad shifting, bad fluid
Owners of 2010 Chevy Colorado, Express or Silverado; or GMC Canyon, Savanna or Sierra, equipped with the 4L60E transmission may complain that the transmission will not make a 2-3 shift, and slip in 3rd and/or 4th gear.
This may be caused by a sticking pressure regulator valve, which may be intermittent.
Check the line pressure per the diagnostics listed in SI. If the line pressure is low or cannot be controlled using the scan tool, remove the transmission and inspect the pressure regulator valve for sticking throughout its travel in the bore, and inspect the bore for a rough surface.
During inspection, the transmission fluid may appear distressed (burnt).
If the valve sticks or if there is a concern about the bore finish, replace the pump cover, disassemble the transmission and perform necessary repair.