We've been using Gabriel Ultras on all our fleet trucks, both Silverados and Savana/Express 3500 service vans, for many years now.
Excellent shocks, nice ride with superior body control. Poster above knocking Gabriel should note that like any other company they make a dog or two. But the Ultras are the bomb for trucks, with a real lifetime warranty.
Many folks think the 5100 B's are great, but on my friends truck they are very stiff, almost uncomfortable. And KYB burnt us a few years back on a set of rear shocks, that won't happen again to me...