[spdbrake]

So your Superformance has a voltmeter and an Ammeter? Are you using a Multimeter for the voltage. If so where are you attaching the meter?
Strange readings as your voltage is climbing the as the Amps go up too.
Normally as voltage increases the amps go down.
Work performed (watts / voltage = amps)
Much like a 110vac compressor needing 20amp CB, and then rewire the motor for 220vac it only needs a 10amp CB.

Are you sure the new battery is fully charged? Is your charger a smart charger? or least the amp reading at the 10amp setting should be reading zero.
Last thing: When this started you had a 3.5yrs low charge battery. Then you pulled the alternator for testing. Is it reconnected properly? Rule of thumb in aircraft maintenance. If you fix a squawk and now have a new squawk. Go back the check what you touched last.