Slip Yoke Clunk Fix....Sort of..
Since Ford will not do anything to fix the horrible clunking that I get at every stop light, I decided to talk to a drive line shop. I told them I was willing to spend whatever I needed to fix this because it drives me insane. They said a new yoke will most likely not fix the clunking (FYI, I have a 1 piece drive shaft where the yoke connects to the transfer case). They said grease is about the only good option for now. They said that GM and some other have starting using nickel plated yokes to solve this problem but that Ford has not as far as they knew. They told me to use a heavy synthetic grease (which I have done 3 times so far and it works for a few hundred miles before the clunk returns) on the splines. I got tired of removing, greasing, and reinstalling the drive shaft (which takes me about 15 minutes now) so I decided to install a grease fitting to make my weekly greasing much easier. All that is required is drilling a hole about .75 inches from the rear part of the yoke, tapping the hole, and screwing in the fitting. Took me about 15 minutes and it works great. Now I can grease the yoke in a few seconds. The only issue is you have to move the truck until the fitting faces down so that it is accessible when you want to grease it. I took the truck on a 200 mile trip today (some 4 wheeling included) with no ill effects.
This isn't really a fix, but it is better than removing the drive shaft every time I fill up with gas. Just thought I would share and hopefully help someone else out.
2015 F150 Lariat FX4 3.5 EcoBoost SuperCrew