Electrical issues....

[sandking]

2005 Chevy Suburban 5.3l, fully loaded with every option available in 2005. The problems are this:

The volt gauge is pegged. All other gauges good, battery and alt are good.

The stereo/navigation and dash lites stay on when you turn the ign off and with the key out and the driver door open, but if you open the rear door, they turn off. Sometimes it works with the driver door as it is supposed to.

Last night, the heater would not turn on untill the truck was in drive. In park, no air blowing.

I know there is some weird electrical issues going on somewhere, but where do you start? The burb came used from a small no name dealer and its out of the factory warranty. The dealer says they will repair, but I want to make sure I know the issue going in before hand. Any advice besides giving it back? Thanks.