Haven't started delving into all of the possible problems, but I'd like some feedback on things to look into.

Truck starts up and, during an idle, will be feeding 12.5-13 volts to the battery.

Problem begins when I'm driving it around. Voltmeter (tested and good against a multimeter) climbs exponentially in relation to the RPMs I'm currently at. There seems to be no regulation on how much voltage the alternator is sending out. Cruising at 2000RPM, the voltmeter reads 17 volts and might actually be pegged. Haven't ran a voltmeter simultaneous to find out actual value. Just know that it's too high.

Does this sound like a bad voltage regulator? I haven't tried another one and I can't verify that this one is good. I do know that I've got a good ground at the regulator.

Thanks in advance.

Most any parts store can test your VR.

Not at the Kragen/O Rielly or Auto Zone in my town. Maybe NAPA or CarQuest?
I have had Voltage Regulators give the symptoms you describe... overcharging. If you replace, save the trouble and buy a good one. They also need to be grounded. I once tested a pile of used VRs on a car and found that after several in a row tested bad, they were actually okay if I grounded them with a jumper wire. I was testing them while laying on the inner fender.

Unplugging the V/R should disable the charging, if it doesn't than the problem isn't the regulator it's either a issue with the alternator or the green wire from the alternator to the regulator... The regulator grounds the field windings of the alternator through the green wire, the blue wire going to the alternator provides a switched 12v power supply to the field windings, the same blue wire also goes to the V/R providing a "sense" wire that the regulator samples to know the system voltage... So a bad ground or low voltage to the sensing wire at the regulator can cause over charging, a grounded green wire from the alternator to the regulator can cause overcharging or an internally grounded field winding in the alternator can cause overcharging..

Thanks again for the help felluhs. As suspected originally, the voltage regulator took a crap. Installed one I had laying around (circa 1977) and the voltage is a steady 14.3 while cruising. It does dip a little lower (12.8) at idle, but as soon as I'm off idle, it picks right up. My idle is a little low at around 650 rpm in gear, so that might be why.

Thanks again