2000 Oldsmobile Bravada No power at all

The car was running funny with such things as the gas gauge going loopy, the radio shutting off, and it was hard shifting out of first and second gear. The transmission people told me I needed a new one. There was virtually no metal when they dropped the pan and replaced the filter and flushed fluid. Yesterday I shut it off and there was nothing. I could not get the key out of the ignition, could not get the car out of park, the entire electrical system was out. I jumped it and it was fine. Shut it off and it was dead again. I am thinking a ground somewhere is disconnected or bad. Any help?