The flasher circuit now has a much smaller load on it then before. Years ago you needed to swap out the flasher in the truck for one that was compatible with LED lights. I'd look into that. I don't know if you can change them out on the new trucks.
One way to get around that was to wire a regular bulb in parallel with the LED lights so there was more current draw. This will make the flasher circuit work properly again. The problem is this kind of defeats the point of putting in LED's if you're trying to reduce current consumption. You still get the longevity and cool look of LEDs.
