I think we are confused about what you have as well!
While you can normally go by the label on the bezel, the only way to know what you have for sure is to crawl underneath your Jeep (from the driver's side about even with the door) and take a look on the transfer case. There will be a round metal plate that will say NV231 (or NP231), or NV242 (or NP242).
If it says 231, you have Command-Trac, which (as has been pointed out), does not have a 4WD setting suitable for high traction surfaces.
If it says 242, you have Selec-Trac, which has an open differential, allowing 4WD full time use.
In any event, you do not want to use 4WD part time or 4WD Lo on surfaces that do not allow the wheels to slip.