GMC Troubleshooting Questions? Ask a Mechanic for Answers
Welcome I'm Chris aka Moose
The PCM computer has detected so far what appears to be a transmission issue and is warning you with the light issues you are seeing. Driving it this way can be causing more damage. Is there any way you can get it scanned and get back with me on the codes. The limited current info is pointing me most in the direction of the range sensor which tells the computer which gear you have selected. Meaning you have shifted to drive and are wanting automatic up shifts but the computer is getting a signal that you have selected a different gear even though the manual valve is in the drive position.
-----------About me and Just Answer------------
I am in my upper 30's, have a wife and 2 sons. I farm, fish, hunt, build, and coach youth soccer. I work on anything with an engine, been to many schools and classes through my 12 years with the dealership to get trained and certified. I try the best I can to share what I know and or have access to with my customers. Please consider I base my questions and answers to you, solely on the information you give me since I am not there to see, smell, hear, touch, or test. I try my best to be here everyday starting at 3pm central. Rating an answer is required. Please let me know if your not pleased prior to rating or if you cannot rate me so I can try to help a different way. God Bless and have a great day.