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?