I've had the Bilstiens on my 96 3500 for 100,000+. Paid $200 for 4 from a place called MacNeils out of the midwest. They usually advertise in Car and Driver, Road and Track type magazines. There ad is usually for those fancy floormats and sheepskin seat covers but they also sell Bilsteins.
As I understand it, the Bilstein's are warranted for life and if 100,000 + on a truck like the heavy front ended Cummins is an indication, they will hold up well. Checked with the tech guys at Bilstein while at the Sema show and they said the shock is still functional as long as you can not compress the rod lower than 0. 75 inch from bottoming out. If you can, then some of the nitrogen gas charge has leaked out.
I can not compare to the Monroe Sensatracs but I first tried the Monro Gas Magnums before the Bilsteins, and they are for sale with less than 5000 miles if anyone is interested. The OE shocks were crap from the beginning. Those came off by 18K!.
Gabriel is supposed to make a large diameter RV shock (but I never could find anyone that had any real tech info)
Happy trucking.
Redram