2005 GMC electrical problems

I have a 2005 GMC Sierra with the 5.3L. Everything has been normal up to yesterday. All of a sudden I started the truck and all the gauges with the exception of the tach stopped working, also the abs and air bag light are on. Now the problem has gotten worse the power window now quit along with the door locks. I've changed the battery cleaned the connections, and had the alternator tested. All the fuses check out good. Could this be a bad ignition switch or some kind of body control module? Any help would be appreciated.

check the voltage on the wires at the bottom of the underhood fusebox. (the wires feeding the fuses). i recently had a similar problem with an ignition switch, it was only giving 1.86 volts to one leg of the fuse box.