Interior dome light not coming on anymore

For some reason, the interior dome light in my 2003 GMC 2500HD SLE 4x4 is not coming on when I open the doors, or when I shut off the truck. It used to, up until the other day. If you entered the truck,
obviously the lights would come on. But, when you'd shut the truck off, the lights would come on and stay on for a period of time. I can use the override switch to turn it on, so it's not a bulb/fuse problem.
I plan on having the dealer look at it in a week or so when I get the oil changed, but I was thinking if it was something stupid I was overlooking, I could save myself the embarrassment.
Thanks,
Tony
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have u pushed in the button below the light cluster that disengages it??

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