I know this might be a dumb question lol but i am curious, so i jacked my car up in the back today and spun the tires and both of them were moving at the same time. so is that like a posi or a locker? because i got my jeep from a used car dealership and it seemed all stock.

 

moving in the same direction, or one forward and one backwards?

Moving in same direction would be locker, one forward and one back is open diff.

 

one forward and one backwards. and what does open diff mean?

 

you have an open diff then.
With an open diff, the tire with the least traction will spin, causing you to go nowhere...
Limited slip sends some of that power to the wheel with traction through clutches or gears
a locker physically locks both axles together, causing them to turn at the same speed no matter what.

 

ok thank you lol just one more question is having an open diff bad?

 

for off road yea, but it has on road respect so your not always squacking them

 

It does seem a little large, have you tried exercise. Sorry by the heading, I couldn't resist.