I have a 2008 Expedition (68k miles) with towing package that likes to clunk, going uphill, right before it downshifts from 6th to 4th. It's a double clunk right before it downshifts. RPM is anywhere between 1100 to 1500, mph doesn't matter. Cruise on or off, I have same problem.Definitely feels like it's coming from the rear of the truck.

Checked the transmission fluid level and it's fine. Haven't checked the drive shaft for play yet. What am I looking at here?

 

Take it in to the dealer. The tranny might need to be reflashed. There were many software issues with these.

 

Ended up being 2 bad plugs with cracked porcelain. Number 8 plug decided half of it would stay behind.

 

you should already change the rest of the plugs since you replaced 2

 

I did all 8 at the same time.

 

oh im sorry i must have read it wrong