i'm guessing it's the actuator on the front differential. it's not working so it's not engaging the front axles. the reason you feel something in 4l because that drops the gearing down real low on all the axles. what your feeling is the increase in torque from the rear. figure out why the diff actuator isn't working... or even better replace it with something like this http://www.quadratec.com/products/52435_0100.htm .these jeeps are pretty simple as long as something is not noisy or jammed it's probably something simple.

 

Thanks xjred96 ... and cruiser54 I have something on my passenger side but it looks a little different than that... I posted a pic of it earlier in this chat