Hey man, I have the exact same issue after installing my pro-comp 2.5" front leveling kit. I think I *may* have found the issue and will post back this evening once I check **** out.
In pro-comp's instructions, it says to torque the lower shock bolt to 325ft/lbs, Ford's spec is 406... I think pro-comp got lazy and didn't bother updating the instructions for the '09 up trucks. Also, Ford's procedure is to torque this nut with the wheel on, and the weight of the truck on the ground or else "incorrect clamp load and bushing damage may occur"
I torqued mine with the axle in the air to only 325, and I have a noticeable looseness over slight washboard/gravel roads and I hate it.
I'm going to (with the truck on the ground) remove the nuts from the lower shock bolts, apply anti-seize, and re torque them to 420ft/lbs tonight.
Talk to you soon.