Alternator problems

[Cheyenne350]

Im confused here with the problem I just started having not too long ago. I have 69 Chevy c10 with a built 350 ZZ4 heads, 750 demon carb XE284H comp cam. Alternator will drain the battery while truck is running and will drain it completely dead. I’ve done the trick where you turn on the truck remove battery alternator will stay running but once put into gear engine dies.

I’m guessing it’s the alternator but asking around will say I have a short somewhere. Alternator is a 14 volts 100amps, asking summit racing tech support advice me to get a 12volts 100amps and that should solve my problem. Any help here would be appreciated thanks!