I've looked at the slip yoke threads on here, but none seem to be what I am experiencing. This just started recently, I have 76,5xx miles.
When traveling along on the interstate, and I slightly accelerate say 4-5 MPH I get sometimes one, sometimes a couple thumps underneath. It doesn't happen every time.
It doesn't do it coming from a dead stop, only when moving at speed and accelerating. The transmission is in overdrive, and it is not downshifting.
Does this sound like the slip yoke problem? It's what I'm leaning towards and have ordered the grease to do the fix posted by FordTechMakuloco since it is inexpensive and worth a try but wanted to get some other opinions.
Thanks!

 

Could be. Any time the yoke wants to slip while its transmitting torque, there is the possibility for it to bind and cause a click/thump/bump/etc when it lets loose. Greasing the slip yoke is a cheap and relatively easy fix, but the OEM PTFE grease doesn't last long for most people. Its worth a shot to see if that helps.

I have a thread where I coated the slip yoke with a product called NeoLube instead with great results. I've done it for many customers at this point and a few members on this site have tried it too. It works way better than the Ford grease, and lasts way longer too. Check it out, if interested: https://www.f150forum.com/f38/anothe...ke-fix-382555/