I've been suspicious about my new camera and whether the autofocus was accurate in critical situations. Before I head out for a 3 day assignment next week, I wanted to run some tests.
I use a specialized lens alignment rig to check my auto focus accuracy, but you can probably cobble something on your own. What it involves is accurately getting your camera and subject planes aligned, shooting wide open, and seeing if you're off. The high end cameras have the ability to set a correction factor in them, and set that for an individual lens, and even at different focal lengths for a zoom lens.
The LensAlign rig has a clever sight-through design that solves the alignment issue for setting up the test. The tilted ruler gives you a scale to measure how off the focus is.
My suspicions were correct--my 70-200mm was forward-focusing by three ticks on the correction scale. There was no problem with my other camera bodies, just the new 5D MarkIII. It's all good now.