Good trucks by today's standards

it could be an issue with your multifunction lever. Disassemble/inspect/clean.

Or the flasher module. Maybe these will help ...

Turn Signal/Hazard Lamps

The IGN E 10 A fuse in the underhood fuse block supplies battery positive voltage to the turn signal/hazard switch assembly. The FLASH 25 A fuse in the IP fuse block supplies battery positive voltage to the turn signal/flasher module and ground is supplied at G200. When the turn signal switch is placed in either the left or right position, a voltage signal is completed from the turn signal switch to the turn sign/flasher module. When the hazard flasher switch is activated, a ground signal is completed from the turn signal/hazard switch to the turn sign/flasher module. The turn sign/flasher module then sends an on-off voltage signal through the LT TRLR, RT TRLR, LT TURN or RT TURN 10 A fuses in the IP fuse block to the appropriate turn signal or to all 4 fuses for hazard operation. The instrument panel cluster (IPC) indicators receive voltage from the LT TURN and RT TURN fuses as well as the DDM/PDM for the mirror turn signals. The DDM/PDM has no function or control of the mirror turn signals other that a pass through connection for the circuits. The audio chime is also activated when the turn signals are on. When the hazard switch is pressed, all turn signal lamps will flash including both IPC turn indicators. The front turn signals are grounded at G100. The rear turn signals are grounded at G401.