Take the truck to your Ford dealer who will reprogram the BCM for LED's.
The SVE specifically addresses the front turn signals. It's unclear on the rears and you may still need resistors in the rear lamps. If the BCM sees a minimum of 700mA current draw, it won't think the lamps are out and enter "fast flash" mode.
What I am going to do is have the BCM reprogrammed and then try red LED's in the rear. If they fast flash, then I'll buy and add the resistors.
Last note: I know the SVE is for incomplete vehicles (sold to ambulance, etc. builders) but it should also apply to our trucks as well.