In addition to heavy duty jacks make sure they are resting on solid ground, last month I almost got pinned under my truck as the asphalt drive gave way and stands collapsed, it had been raining week before and sand under the asphalt must have been wet and base of the stands cut through the upper layer and truck shifted & stands slowly collapsed under the truck, I had prescence of mind to put the removed wheels under the frame and truck settled down on those instead of my legs. I usually put 3/4" plywood under my stands to make a firm base, got lazy and didnt as I did not want to make a trip to lowes and get some wood, figured it was cool enough the asphalt would not be soft, and almost hurt me or the truck as result, bee careful folks these things weigh more than you think.