If i'm suspecting a bad shock, i usually will remove the lower bolt of the shock and see if it compresses way too easy, i have had a bad/broken shock on the front once, and it did not do this bouncin down the road thing as previously mentioned, it just felt like the truck would bounce in a weird manner when a big bump was hit, basically like one side was too soft or something.
That is the best way so that i have found how to check out the shocks, doesn't take much time, just need the motivation to work on it. /forums/images/graemlins/thumb.gif