2004 F350 V8 6.0L Diesel totally drained battery so checked alternator and it's okay and checked the batteries and okay What else could it be?

Be sure to chek for ground outs. That will drain a battery in no nime. Usually doesn't happen but chek to make sure nothing is crossing the poles when the hood is down.

Check around starter, and into the fendors. These are typical ground sites.