With respect to the comment about BS, yes, there is some, but not much. The stickies listed at the beginning of this part of the forum contain a lot of very fact specific info and quite a few time sheets and dyno runs. Check here:
http://www.titantalk.com/forums/showthread.php?t=18365
There is a lot of data on unmodded trucks and a good bit of very objective info to check out. And . . . while the rear diff with the Big Tow package, is, indeed, 3.36 to 1, the gearing in the tranny produces a very low first gear and closely spaced gearing, especially in the first three gears, which produces an effective gearing equivalent to 4.10 to 1.