Bilsteins x4...if you're looking for a good HD shock, very few things are better than a set of Bilstein 4600s. My dad has had them on his 3/4-ton Silverado Duramax that we've used for towing our 13,000 pound fifth wheel, and after almost 100K on the shocks they still work just as well as they did when they were new. They may be kinda pricey but they are well worth the investment.