Chaffers used a 1/2 Snap-on air gun to remove the lower U-bolt nuts. A little trick I like to do is leave two of the four nuts on but almost to the end so the axle is supported while you remove the other side. If you are working alone, grab a jackstand and support the opposite end that you just loosened up. Remove the four bolts and now walk to the other side. While supporting the axle with one arm, remove the two nuts that were left loose. The axle should now be free to remove from the vehicle. Be careful, it is heavy.