Mine worked fine till I swapped my cluster for another one that had a different style gauge font that I liked. Everything else worked great even though gm said based off the vin the cluster didn’t interchange. So you either have a bad cluster or your cluster has been swapped. The cluster carries the mileage memory

New style font I liked with the - - - oil life error that can’t be reset
so if your cluster has been swapped someone prolly did it to alter the actual mileage of the vehicle sadly.

 

I have a similar problem, not sure if it's related or not. In my case what happened is the value that the oil life reset to kept decreasing. IE it went from resetting to 100% to 82% 63% and so on until it now resets to 0% but I do have numbers not ---.
I never got any feedback on the problem. I do know that in my case it's not in the instrument cluster. It's in a different computer somewhere. I swapped clusters between my 05 & 06 Tahoes and it stayed with the vehicle.
My profession for the past 45+ years is component level electronic diagnosis and repair. (radio engineering) To me what this looks like in somewhere there is a circuit that is being charged to a voltage and is being discharged over time at varying rates dependent upon operating status & conditions. If that is true it would seem that the circuit has failed to a low voltage point.

If this works, this is my previous thread about this: https://chevroletforum.com/forum/tah...t-issue-92942/