Sorry, I can't PM you as I do not have enough posts.
2001 - You have LCI taillights - DUH! Nevermind what I said about the bulb holder - that's for pre-LCI cars like mine - if the fault is in the LEDs and the problem is not in the connector, you'll need to replace the complete taillight or repair the internals.
Still true, however the possibility of a bad connection at the connector. Possibly corroded or burnt. Carefully remove the connector and inspect for corrosion or other damage especially on pin 8 which should be a gray and white wire. I would back probe between pins 8 and 3 with a meter and check the voltage drop compared to the driver side (pins 1 and 4 on the driver side) which should be B+. If it's the same, the resistance is in the connection at the taillight or internal to the taillight; if it's different (less on the passenger side), then the supply voltage is low, or the ground is bad. Check supply voltage at pin 6 to a known good ground (straight to the battery negative post) and also for resistance in the ground circuit between pin 3 and battery negative (should be 0 volts).
LEDs don't fail with reduced output. I'm certain it can be repaired, even if you have to dissect the taillight. Let me know what you find.