Here is one way to get smooth text scroll:
Draw the textfield to bitmapdata, and scroll/tween that bitmap instead.
set fraterate 60 (if your app can achieve it)
set stage.quality to LOW to drop anti-aliasing and boost the performance/framerate.
Don't cacheAsBitmap, just draw and place the bitmap on the display list.
note: the quality of draw() relies on stage.quality, so until adobe changes this, you need to set stage.quality HIGH for the draw() call, and then set to LOW for the remainder of the time... if you choose to run in LOW quality as i recommend when using the gpu rendermode.
If your app is slim enough to achieve 50-60 fps, this will appear very smooth, even at lower FPS it might be ok.
I don't know if your app is built around cpu rendering already, but blitting with copyPixels should be with CPU rendering, and it is not as fast as the GPU mode with simple bitmap manipulation.
I know this technique may not be ideal, but its one of the smoothest way to scroll text that I know of.
Also, I have not really tested stage3d on mobile much except simple starling tests, starling and/or stage3d might be better. (rendermode=direct) In the near future stage3d is expected to be the best performance option on air for mobile.