Last fall I purchased an 02 DMAX w/52K mi and an ATS juice. It now has 58Kmi.

Just last week the gear selector indicator became erratic...
It always seems to show 1st & 2nd gears properly, but usu when in park, rev, neutral, and drive the indicator does not light or show any selection.

At the same time this problem occurred, I noticed the auto door
lock function is funky too. The doors usu (but not always) auto lock just after leaving park into reverse or any other gear. If I unlock doors manually they will auto lock normally after reaching 15+ mph. Fuses check good. Any ideas? Thanks, Steve.

Dont take it to the bank but id bet NSBU switch....Neutral safety backup switch

My dad just had the same thing happen on his '02 Duramax. I think they had to drop the tranny to fix it the switch

mine did the same thing, then finally only had reverse and 3rd gear indicator light, replaced nsbu and all is fine. about a 30 minute job and you can get the part from one of the vendors on the forum here. Thanks much to all the folks on this forum with all the photo's and info on how to do this. Great Place

Guaranteed it will be the NSBU switch. Those are the first symptoms. Erratic shift indicator. Does not move when moving lever. They have a new improved switch. They do not have to drop the transmission, it is mounted on the side. If you are not mechanically inclined take to dealer. Do not let it go for long, When it goes...it really goes meaning the trans will not shift properly and stick in gears. It is exactly what mine did.