2005 Silverado-Durmax: electrical problem

[Coley]

Ok, I have an 2005 Silverado 2500HD with the Duramax drivetrain...a great truck overall.

However, I'm starting to have a weird electrical issue...actually there are a few, but one is a bit more annoying than the other.
First one is that now when I shut the truck off and exit it, the dash lights and radio often stay on. So one of the choices is to manually shut the radio off or dim the gauges to zero.
....but, if I go around to the passenger side and open and close the door on that side, they shut off...as they should.
I am aware that there is a 10 second delay before this stuff sometimes shuts down but that doesn't often happen...sometimes when I exit the store and come out to the truck the radio is still on, lol.

Anyone else have this happen?

the other issues have been the slow demise of initially the speedometer and then the tachometer...and the dimming of a few of the dash gauges.
This is not the problematic one tho'.

Any insight on this guys is much appreciated!!

Regards,
Coley