Measuring a frame out aint too bad. If you arent goin to have a shop check it for ya, you can measure it out with a tape measure. just measure from symetrical points from each side to a set middle. Measure in a X pattern between the different points in the frame. The numbers should always coincide, but there is a set amount of lee-way as far as a bent frame. Such as measure the distances between framerails, and to the ground at different points, and to the body itself. Can lead you to find other problems as well with cab mounting and bad body mounts. Its not hard to figure out if you think about it for a sec, which angles and measurements should be the same and which will of course be different. I know measuring under there has helped me find bends in lift kits, and broken components. Just fyi, otherwise ide have a frame shop check it to within tolerable limits.