If I read it right, and I could be off, if you swap the 04 face for a 2005, 2006 face, you need to rescale the tach for accuracy and to account for the higher red line. You can fix the speedometer and MPH light but I had that done back in early 2005 when I had a cluster issue on my drive home when I bought it new. The dealer had to wait for GM to release the software update for it.The tach? I thought the problem with the 04s was the speedometer settings and the MPH light searchlight brightness. Unless you are just talking about resetting the redline.