Originally Posted by jimspinnin
It was the plug!!!
You need to remember that fast turn signals mean a bulb (or two) has burnt out (or the plug open) which reduced the current load on the flasher.
Slow turn signals mean a short in the circuit which increases the current load on the flasher.
Since you've taken care of the plug, next time you notice a fast indicator, take a turn around the truck to inspect the lights and replace the one which went out.