No, you don't need load resistors! That will cancel out the energy savings of the LEDs (one whole reason why the world is switching to LED). You just go to the auto parts store, or the semitruck store and buy a Solid State electronic flasher to go in your steering column. The fast flashing is a form of 'bulb out' warning to let you know that a bulb is out (thinks bulb is out since LEDs don't draw crap for watts). Mine flash normally now.
More experienced electronics savvy guys can soldier in a variable potentiometer that goes where the resistor goes inside the factory Ford flasher and then you can adjust how fast it flashes. But otherwise you can just buy the non-load sensing universal S.S. flasher like I got in mine. The non-load sensing flashers can work on 1 to 10 bulbs and still flash at the same speed.
Here's my LED retrofit I did to my Contour:
http://josch.wilksfamily.com/LEDandMarker/LEDretrofit.htm 
