2002 GMC Sierra, secondary trans cooler line broke, replaced cooler, fluids good but won't shift to 3 rd gear properly.|What to do or check?
Is the check engine light on? You may have to have the codes pulled, if no light then pull the ECM fuses wait about 30 seconds then reinstall them then drive the rig normally, if that did not work then hopefully it is just a plugged filter in the transmission, having it serviced might be money well spent at this point.
Search GMC Sierra 1500 Questions
GMC Sierra 1500 Experts