Investors reduced their overall equity exposure in May for the second month in a row even as the S&P 500 hit a record high, according to a monthly proprietary trading survey from TD Ameritrade.
The firm's so-called IMX Index, which monitors the behavior of the largest pool of retail traders, fell for a second month in value but still remains in the moderately high range.
"There's overall skepticism with the market at highs," said Nicole Sherrod, managing director of TD Ameritrade's Trader Group. "They were still taking profits and seeking yield."
One interesting tidbit after peeking inside their customers' books was the explosion of trading in Tesla, which was the most actively traded stock in their retail pool.
The electronic-car maker nearly doubled in May as short-sellers were forced to cover after stellar reviews for the company's flagship vehicle, the Model S. Founder Elon Musk said at its annual meeting that he will sell 15,000 units of the luxury sports car this year.
(Read More: Elon Musk: Self-Driving Cars, Hyperloops and a Cheaper Tesla)
"Our traders tend to chase momentum," said Sherrod.