Ouch!!!

 

On newer f-bodies (97, 98+?), I think the gas gauge is computer controlled to compensate for the shape of the gas tank. On the older ones, of course, 1/2=1/3, and gets worse the lower you go, at least on mine. It'll sit above full for quite a while and then start to drop like a rock.
My speedo is dead on, the tach is 100 rpm high, temp reads 10-30* high depending on where it is, haven't verified voltage though.
Most of the gauges do suck, but when you have the car long enough you know what's going on anyway.

You shouldn't be worried about a high voltage reading on startup, unless it pegs in the red or it stays that way all the time. 99% of the time the only problem you'll have is when the gauge drops too far to the left and stays there...