did you try rotating your driveshaft 180 degrees before having it balanced....often that will fix any vibrations...

 

I would also add grease to the splines, since that's been an issue with some F150s. If you're rotating the shaft, might as well as some grease.

Did you match mount the d/s to the axle? There's a paint dot on the shafts that should be matched to the axle. (at least I think, I know we did this on Explorers)...

 

i will try rotating the drive shaft 180 deg. if this my help its worth trying. i will let you know. try some grease to thanks.