I replaced the original shocks on my 2012 E-350 {Nexus 23P}, at 30,000 miles. Day to day driving you tend not to notice/appreciate just how bad your shocks are getting as the deterioration is so gradual. Put new ones on and Wow! Why did I wait so lo ng becomes the question of the day.
After a lot of research I went with the heavy duty Bilstein's and after 11,000 miles could not be more pleased. I spoke with the folks at Bilstein and Shock Warehouse{who had the best prices on the internet along with excellent customer service}, several times seeking their input. Since we typically run close to our 11,500# GVWR and I often tow my Harley {bike and trailer are 900#}, the consistent recommendation was to go with the heavy duty model.
I am so pleased that we did as the ride improvement and additional stability and control are off of the chart wonderful. The rig always handled well and the ride seemed comfortable enough but the improvement was nothing short of amazing.
A word of caution for you DIY guys.... installing the Bilstein's is a serious PITA. I took the coach to a commercial truck repair center for the install. Two of their biggest guys worked for nearly 3 hours to get them on. The rears were no problem but getting the fronts compressed sufficiently try to permit the install was a serious struggle.
I have made no other changes to the coach other than the new shocks and it drives a like a large SUV. Passing trucks are simply not an issue and in winds up to 35 mph relaxed one handed steering is the norm. Along with the Bilstein's a lot of this ride quality is a reflection of the fact that my tires are properly inflated for the loads they carry and the CAT scale confirms that my weight is properly distributed and within spec.
:C