I have had several of these on Blazers, Astros, and similar chassis, and it is usually the switch. Most frequently, it seems to be related to the hazard flasher portion of the switch. If you exercise the hazard flasher switch several cycles, does the problem change? If you slightly depress or slightly release the hazard flasher switch to position it differently, does it affect the symptoms?
If the turn/hazard flasher module has been replaced and the new switch is intact and was installed correctly you've just about covered it aside from the connectors and wiring.
If it helps, this is the diagram for your system:
