Something else
It sounds like your starter is drawing too much current. Could be a bad starter (internal short), could be a bad starter cable, could be bad connections at the starter or solenoid. Inspect your cable. If it's old and/or too small of a gage, replace it. If you're using one of the old heavy starters, replace it with one of the new light weight starters from a 5.0. I've had cheap AZ solenoids that lasted for years.