I need advice with some inconsistent actions of Voiceover on my iPhone 4s.

I need to use Voiceover when using my iPhone 4s. When reading a text or email, I often need to scroll down to see more of the message. Sometimes, when I tap (once to highlight or choose area) & then tap twice (to activate action), & then hold down on the screen after the 2nd tap, & push up with my finger, the screen moves up correctly & I can continue reading the text. But other times, when I seem to be doing the same exact actions, the "select, select all, cut", or the "copy, delete" or similar options appear in a small black area in the middle of the text. I figure I must be doing something different to lead to different actions, but I can't tell what I'm doing differently. Any ideas? Also, even when I am able to scroll down the page of text, as I lift up my finger, or tap again to start the reading aloud again, it starts reading from the very beginning of the text, repeating itself until it gets down to the "newly-showing" part. Is there any way to get it to only resume reading the part I haven't heard yet? Or to resume reading from any given point, instead of from the very beginning? I already know that a 2-finger swipe down reads from the currently highlighted part down to the end, but in this case it won't let me highlight anything in the middle of the text. Please advise. Thank you for any help you can offer.