I went through this last fall, both my rear sensors were seized and not able to move freely. The truck would look really high in the rear. If i were you i would find out how much it costs to run the code on the computer, it will tell you which sensor is failing if it's just the one. More than likely i would just change both.

I replaced both sensors, arms, and brackets on the left and right rear. The sensors are around $80 each if i remember correctly. They can be replaced by yourself too.