1998 f 150 electrical problem

My 1998 f150 battery light on dash would come on and off while driving for about 1 week. I put in a new battery but the light continued to come on and off. Took it to the local ford dealer and they said the battery was fully charged and the alternator was putting out the correct power. Even after the diagnostic check, the battery light continued to come on and off. Today while driving, the radio, oilgauge,speedometer, tach and lights went out but my truck kept running for a few miles. Then it turned completely off and now will only start with a jump off another car battery. When I turn the truck off...it requires another jump. Any suggestions before I take it back to the dealer?
thanks
Tom Davis