The HF 3/4in impact wrench is the bomb, yo.

1000ftlbs of torque for $99 on sale. Used it and the service air on my M35A2 to change tires.... its one of the HF gems.

http://www.harborfreight.com/3-4-quarter-inch-heavy-duty-impact-wrench-66984.html

Its a 3/4 drive and heavy as heck but I find that 1/2 impacts can and do fall short. Keep it oiled like any other impact tool.