I have owned several Tahoes in the past and the voltage gauge reads 14 volts whencruisingand the pointer stayed put under virtually all conditions, lights on, etc. My 08 Tahoe reads 14 volts most of the time but sometimes when rolling down the highway at 70 mphI see that it is reading about 11.5 to 12 volts, well below the normal reading. A few minutes later it is back to 14 volts.The dealer says this is normal but it sure seems strange to me. Anyone notice this on their 07 or 08 Tahoe?

 

They all do it. Do a search on this forum and you can find the explanation as to why. Basically they cut the alternator when it's not needed thereby reducing, albeit by a small amount, the load on the engine. And as Martha says, "That's a good thing".