I have had a similar problem for several months now, and have never found the problem.
First, it's not an Avalanche, but it is a 2000 GMC Safari. It will suddenly turn off every gauge in the truck, then turn on every idiot light and gauge, and then return to normal. There is no stumble in the engine, no gear change, just this light show that lasts a few seconds. As the truck is being traded for a new Avalanche, I have given up trying to track the problem down, but let me give you a possible fix.
It seems to be electrical, so I had one suggestion to carefully remove and reconnect various electric and electronic connectors. One mechanic suggested doing this with the main computer chips. He felt that it might be a bit of moisture or corrosion in one connector. Although I have cleaned the battery connectors, the various grounds and several other terminal points, I still see this happen - perhaps once or twice a month.
I'm sorry I can't help more. It is one problem I have never figured out...
Michael