To isolate the problem down to its potential cause... Here is some additional information:
(1) It is critical NOT to swap in just 'any relay' (such as the Typical *Clicking* Solenoid Type) into the Slot for the DRL or Headlights. This is because the Low-Light performance aspects of the DRLs is controlled by the Pulse Width Modulation (PWM) happening at 0-7 Volts DC on the Class 2 Network single wire in between the PCM and the BCM.
Thus, only the Special $40.00 Relay capable of performing the rapidly pulsed switching necessary to achieve the DRL performance should be installed in the Power Distribution Center.
(2) When the DRLs are activated, it sends a signal to the BCM which grounds the Circuit at the
G101 Ground Location as described in this On Topic Link below. Check out these Diagrams and then locate-inspect-clean-repair
the G101 Ground for any possible Damage or Corrosion problems in between all of the contact metal surfaces.:
While troubleshooting a bad ground I came across some scans of the service manual regarding electrical ground locations for our platform posted on another site. This includes both short and long wheel base, as well as both 4.2L and 5.3L. Credit goes to Wex...
gmtnation.com