Electrical Issue

GM radios draw a lot more current than other brands so they are more susceptible to voltage drops either in the radio itself or in the car's wiring. In the radio it's bad connections. In the car, you can pull the radio out and connect a voltmeter to the two power wires and monitor the voltage when this happens. If the memory circuit drops noticeably, check for corrosion on the fuse and terminals. If the switched circuit drops, a good suspect is overheated contacts in the ignition switch. When the ignition switch is the problem, usually other things on the same circuit will also affect the radio. Common things are the power windows and heater fan.