Bilstein 4600 are for standard height trucks, 5100's are for trucks have had a lift kit put in them
http://www.shockwarehouse.com/news/images/bilstein-5100-vs-bilstein-heavy-duty.cfmI run the Bilstein 4600's on my 2500HD. Mine is a crew cab short box. I also run a Hellwig rear sway bar. I really like the Bilstein's. I had a set go bad and they were replaced under warranty. I bought mine from Autozone. They kept a computerized record of the purchase.
You will need your original dated receipt or the place you bought them from will have to have you on file if you want to submit a claim on the Ranchos.
To make a claim under this warranty, return the worn-out or defective product with the dated original receipt to the dealer or retailer from whom it was purchased or to a Tenneco dealer for verification and exchange under this warranty.
notice on the warranty claim form for the retailer to submit, it has to have proof of purchase
http://www.gorancho.com/downloads/warranty/warranty_claim.pdfSome folks advocate buying from Amazon to save a few bucks. However, if you have a set go bad, if another retailer doesn't want to deal with the hassle of the return/swap out, a person could be out of a shock while trying to get Amazon to work doing a warranty swap out.