To see if you have limited slip, put the truck in neutral, chock the front wheels and jack it up so that both rear wheels are off the ground...no emergency brake. Go turn the passenger wheel clockwise and watch the driver's side wheel. If it starts turning counterclockwise, you do not have a limited slip rear. If the driver's side turns the same direction as you're turning the passenger wheel, then it is highly likely you do have limited slip in there. Also there are codes cast into the rear end (and some will be stamped in). They'll tell you. Please see here:
https://www.chevytalk.org/fusionbb/showtopic.php?tid/263465/ 
