I'm having the same issue, I replaced my flasher unit and still nothing. The flasher relay is located just to the right of your right knee if you're sitting in the truck. Easiest way to find it is to pull the center lower dash panel (with cupholder) out and its on the far left at the top. You can reach it with the panel on but it can be difficult to find without seeing it
If when you turn your turn signal on nothing happens - the indicator on the dash doesn't even light up -- Check fuse 27 in the central junction box...that's a direct fuse for the system. Besides that, and your flasher, the multifunction switch could be at fault.
Last, do you use a trailer towing harness connector for this truck? You may have some issues with the wiring there.