5.0 electrical problem

i am having a problem with my electrical system. Im going throught batteries and altenators on a regular basis.The one think i notice is that the volt gauge goes up and down with the revs exactly.Its almost like the car is running off the alternator alone.I have a new battery and altenator.could there be a short of a bad unit of some kind. any help would be greatly welcomed.

thank you
mike