Check the tightness/cleanliness of the battery terminals, and have the battery tested too.
The positive terminal on my 04 Silverado loves to gradually work it's way slightly loose about twice a year, and the dash lights flickering is always my first clue it's happened again.
It never "seems" loose, never not starts, and usually only takes ~1/4 turn to make it fully tight again, but each time I've retightened it has 100% eliminated the dimming dash lights issue.
Never once had this problem with the side battery connections loosening on the Vette, but it's gotten me about 5 times on the truck over the years.
