http://www.democracycorps.com/National-Surveys/
Same polling company that gave Clinton +5 in Florida last week.
This more or less matches what's been said in this thread. Trump's not gaining significantly, Clinton is losing votes. Those are people who were clearly willing to vote for Clinton, so they can be won. It's just a question of convincing them to get back.
Trump has a much smaller pool of people who are clearly willing to vote for Trump but haven't yet committed to doing so. That's his ceiling.