Quote Originally Posted by Boominburban View Post
Thoroghly clean your throttle body, if that doesn't work, have the PCM reprogrammed to increase idle speed.
This^ Clean your throttle body and MAF sensor.

Some of those posting are pretty intelligent, but they're full of **** when they say 500 rpm is too low. I bass hard and my dual alt's regularly see 400-600rpm at idle after dropping from 650rpm. Obviously I lose output, but nothing like OP is seeing. Yes, they're stock pulley's

I have the exact same engine as you, and two alternators so much more load. One DC Power 270xp and one stock ad244. If you need another alternator to test go get one from a junkyard for less than $50.

Your alternator has a problem. When you pull it off and swap the other in, pull the plastic cover off the back. Look at the brush holders, pull them off if you have to. I bet they're either melted or making poor contact. Other than that the voltage regulator or diodes are fucked. Don't ask me why, I don't know. This isn't the first time I've heard of someone getting a mechman alt (this is on a silverado forum) and having issues. Mechman argued with him for 5 MONTHS before they let him send it back and what do you know? They found a problem with the alternator. Go to an alternator shop if you have to, mom and pop alt shops are the ****

VERIFY FIRST that the alternator is bad, then send it into mechman detailing what you've done to troubleshoot it, and the issues you're having. Be sure to verify voltages on the wiring into the alt. If it's two wire (1 is the positive post, 1 is in the plug) the wire in the plug needs to be between 10-13v. If it's below that the alternator won't excite, if the alternator won't excite you won't get any output and you'll see the 10v you're talking about.

Based on your location in topeka there's two places:
The second only looks like a battery sales center