I have a 1996 3500 dully with v10 2wd was running then all lights came on then just shut down what could it be?

suspect a bad alternator due to a bad battery~ to start, clean off the brass cable end of the Black battery cable as it attaches to the frame and chassis...wirebrush the chassis to renew the ground potential...with your new battery, you'll be off and running~ (if the alternator is still okay~)

relays will drop out, for example the starter or (ignition relay) responsible for your ignition spark and the fuel pump...tho not as fussy for correct voltages does have a relay that enables it....a reduced voltage will drop out the relays leaving you stranded~