Bobatwarsaw; this link says the factory/accessory tach should be a 5K and not a 6K unit. So I don't think it's "correct" but still a nice addition especially if it does not require the transmitter box.
http://6066gmcguy.com/cluster.html
...and another link about the cluster I got off EBay. Look at the different fonts used and I think the 5K numbers have a slight green tint.
http://6066gmcclub.com/showthread.php?t=48609