Almost every ranger has that drivers side sag, unless it's been fixed by the owner. It's because there always tends to be more weight on the drivers side that the passenger, so over time the sag develops. The weight of the fuel tank, battery, and driver are all significant factors.
BTW, your shocks don't provide any lift, or force upwards. Their job is simply to dampen the spring. It's impossible that one side is sagging because of worn out shocks.