In 2wd, its suppose to apply some torque to keep pulling the truck forward. Usually not enough to have both spinning. Unless they are both on ice. Posi-lock will make both lock and turn equally.
In 4wd, it depends on traction for the front vs. rear. If the front is spinning and one rear wheel is spinning with only one rear wheel that has traction. With l/s, it should still be able to pull forward some.
Check the rear diff tag. It be will labeled if it has l/s installed, plus the diff ring size and ratio. something like "l/s 4.10 8.8" or "4 L 10 8.8". Or check the axle code on the driver's door placid card. The axle code should begin with a F or R.