You indicated your donor alternator came from a Denali Envoy...What year and engine. If I look at GM eSI, the 2001 Envoy / 4.3L / 4X4, the generator turn on signal (RED) comes from the PCM to "L" terminal (B on connector) while the (GRY) also goes into the PCM from "F" terminal. Class 2 serial data turns the dash light on w/gauge.
Now, going a little newer, say 2003 Envoy 4X4, like most of the LS engine charging goes right into the PCM for (RED) alternator turn on, while (GRY) is duty cycle to reduce load and increase fuel economy. So, several differences depending on year.
Your voltage reading is correct with OEM regulator, as when cold, voltage goes up, warm it goes down. The published working range is 13.2 - 14.6 volts. Ass of 2009, GM had 32 different voltage regulators and choose not to sell them as it would led to confusion w/ improper operation.
If you go aftermarket, their are quality designed voltage regulators that have two specs...turn on time & set voltage. So, you could get 6 seconds before charging and a set voltage of 14.6. Check out alternatorman.com for I.D. and upgraded parts like heavier diodes on copper plate rectifier bridge. Coupled with a choice of regulator, you could safely get 200+ amps.
It sounds like you got it working, just understand the temp issue vs charge rate. This is the reason for the wire-wound-ceramic resistor found inside the older Delco 10SI and other models. Bench charging is the same with "High" setting for cold and "Low" for warm / hot.
Voltage regulators, ignition modules, etc., a lot has changed but you get what you pay for. The photo below is a 20 year old sample of a popular brand ignition module as built in the day, compared to OEM Delco. Surprise!
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