Its been quite a few years, but when I didn't know any better, I put KYBs on a car, and was annoyed that they were bouncy in less than a year. on the recommendation of the shop I was bringing taht car too, I gave Boge/Sachs a try, the ProGas series, and those were awesome and lasted a quarter million miles. Now that was back in the early 90s on a late 80s VW Jetta, so none of this is really applicable to the shocks on an Expedition.
My last truck, a 2002 Ford F250 diesel longbed 4x4, I installed Rancho 9000XL, which are adjustable, they worked quite well and smoothed out the ride of that 9000 lb beast, but that was a live axle leaf spring superduty truck. However, I don't see any Rancho products for an Expedition, just the F series and Ranger trucks.
My Expedition has CCDs so I'm afraid I'm stuck with replacing them with more CCDs. I'm not sure how to tell when they are sufficiently worn out to justify the replacement cost.