94 GMC Sierra Low Voltage

 I am going to install a BOA 165 R/S on a 94 GMC Sierra but it always seems to start and maintain a low voltage condition until it warms up alittle. I don't know what is causing this - alternator replaced twice and always seems to test as ok off the vehicle. Any ideas as this unit uses vehicle voltage to disconnect the starter after the vehicle starts...

How low, is low?

It will run from what looks like 10 volts to maybe 12 or so. It is hard to tell by the dash gauge. I thought maybe it was the gauge, but if I just fire up the truck and drive off, the lights will dim and get bright  and dim again for a couple of minutes to 10 minutes depending on the temp. So far the low voltage light has not come on.