[andyg]

A torque multiplier will be more likely to break studs than an impact. The jarring action from the impact will go a long way toward breaking the bolt loose without snapping them off. I restore antique farm equipment (very rusted/stuck). I have found that the rattling of an impact will loosen stuck bolts that brute force would have broken. Before you give up on the impact wrench make sure that it is working at its best. Give it a shot of air tool oil not wd-40 or some other stuff. Oil helps to free up a slow air tool. Many impacts have adjustments to regulate the speed. Make sure it is adjusted for MAX power. Make sure that you have adequate air supply. It takes air pressure AND volume to operate an impact wrench. Many people try to run an impact using a small air hose thus starving the tool for volume. If it has a 3/4" inlet then you need a 3/4" hose and fittinngs all of the way back to the tank.
If the nut or stud still will not loosen then I have another trick. Wack it with a BFH! You can strike the nut on the flats a few times and a lot of times it will come loose when you put the impact back on it. I like to hit the studs on the end a few times. They are hard to reach with a hammer so use a piece of steel bar stock placed against the end of the stud. I have gotten lots of stuck fasteners with a few good licks with a hammer.
To help prevent trouble a second time pay attention to how tight you put the lug nuts on. Tire shops should use a torque wrench. You do not need to tighten the lugs to your limit or the tool's limit. Lots of lugs are simply put on to tight causing lots of trouble. Don't let just any monkey work on your rig.