Here is what it said...

Evap Emission Control System Purge Valve C Fault

What does it mean?

 

Circuit fault. What is the actual code?

 

Code was 0443 which reads: P0443 Evap Purge Solenoid Circ

I recently chaged the a/c evap. core and heater core. The a/c is still completely uncharged. Could this be the culprit?

 

Nope. PCM doesn't care about whether the A/C works or not.

Your purge solenoid is up on the passenger side, toward the front, right in front of the wheel well. PCM thinks there is an issue on that circuit.

There is a factory service manual for the 01 trucks in the faq section here, I recommend you download that, and have a look. At least, it can give ya pics of where things are. Problem might be obvious......