Speedometer, Tachometer, Odometer don't work. Transmission won't 'auto-shift'.

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NavyGeo

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Hey everyone, I'm Rick Baran. I'm a retired sailor who owns a 2000 Tahoe Z71. I posted this problem on the sister forum(TahoeYukon) but didn't get any replies at all.

As the title states, my tachometer, speedometer, and odometer have stopped working. My transmission will shift into/out-of Park, Reverse, Neutral, and 3rd manually, but will not up- or down-shift with the lever in "D". My transfer-case appears to shift normally(I have the electric switches on the lower dash to the right of the steering column).

Once in a while(maybe 1 in 25 starts) EVERYTHING will work normally for a few hundred feet up to an entire day's driving(25-30 miles).

Anyways, I have been researching on our interweb, and decided to replace the two Speed-Sensors on the transfer-case. That had no effect whatsoever. I also disconnected the battery and checked ALL fuses with no change.

I read that the VSSB(?) was located behind the glove-compartment. I cannot locate it behind the passenger's glove-compartment. I don't have a wiring-diagram nor do I have a component-location diagram, so I'm having difficulty proceeding any further in troubleshooting.

Do any of you have any ideas as to how I should proceed? I've read several forum-posts discussing the possibility of a bad Ignition-Switch. I've also read about the VSSB, which I take it is a sub-computer and not the big clunky heat-sinked box on my driver-side inner-fender?
 
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