My 2007 5.7L does the same thing when it's cold and always has. I've just gotten used to it. Toyota did issues a TSB for the Tacoma to reflash the transmission control to allow better shifting at low speeds. Perhaps they will eventually do this for the Tundra. Reprogramming is most likely the only thing that will work.
My truck does the same when it is in "open loop" mode. Really sluggish from 2-3 upshift.