Ford F-150 (2004-2008) :: Odd Screeching Sound Under Relatively Heavy Throttle - Driveshaft?

I have an F-150 Heritage 4.2L V6 Manual 4X4 and over the last few weeks have notice a couple of odd things. First I noted an odd screeching sound, similar to a rock caught in the break drum, but it seemed to be coming from under the cab/bed, not a tire. It only seemed to show up under relatively heavy throttle, which I thought was odd. I went through a car wash with a good under carriage spray, and the sound went away.

A few days later it snowed and the sound returned. I don't know that it's actually related...but that's how the weather went... Now, when I let off the throttle and the engine holds the truck back there is a "thump", and when I reapply the throttle, it thumps again. If I press the clutch in first, then release the throttle there is no thump; so I assume this is something with the drive shaft.

I climbed underneath and found that I do have some play in the shaft, I can twist it a tiny bit so I know that I have play in the shaft which (and I am NO mechanic) I assume is not normal. I can see the shaft turning all the way to where it goes into the back of the transmission so I assume the play is coming from the rear yoke?

I thought I could replace the yoke relatively cheaply but I keep stumbling across posts indicating that with this particular set up, I actually have to replace the whole drive shaft. What I could be looking at, and what my options are?