So, I think I know what you mean, and I may have experienced the same thing. Does your Expedition have CCD?
I thought I was going crazy, but I swear that when I have tire balance issues the vehicle rides very stiff/rough. I've noticed it a few times:
1) When I first drove it off the lot, I found it was pretty stiff, but got used to it. I noticed that over 70mph the stock tires were out of balance. I got them road-force balanced and I swear it rode 100% better in all conditions, not just over 70mph.
2) I've been going back and forth with TireRack over a set of winter wheels/tires that they can't get right. Seems to be an issue with the hub bore on the wheels being too large and the wheels don't center properly (~87.5mm vs 87.1mm). If I hand tighten each lug by hand 1/4 turn at time, I can get them centered, but they go out within a day or so. When I do get them centered there is a noticeable difference in ride quality and as they off-center the ride becomes very stiff.
So, I wonder if the CCD is noticing a wheel or wheels out of balance and translating that into road quality - messing up CCD?
Riley