Globally, there have been shifts as well.
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The U.S. indexes have been among the leading performers this year, but there are signs that foreign markets could be stepping up.
The German DAX broke its 50-day moving average with a 4.6 percent gain last week. Markets in Italy, France and the UK also registered gains in the 4 percent range.
Citigroup has made some sector shifts in preparation of a changing market.
The firm shifted energy to overweight—a move that hasn't paid off so far as the sector is off 1.4 percent and has been the worst performer this quarter in the Standard & Poor's 500.
But it has held the position while downgrading food, beverage and tobacco to underweight. The firm also has cut allocations to transportation and telecom services.
Tobias Levkovich, Citi's chief market strategist, warned that conditions are changing and stocks could be unpredictable going forward.
"We continue to believe that (the second half) may prove more challenging but a summer slump driven by the old 'Sell in May' adage is not necessarily in the cards," he said in a note to clients.
Citi is holding to its 1,615 S&P 500 price target, but Lefkovich said the index could exceed that level before dropping below and then rebounding again.
"Valuation remains attractive, while implied long-term earnings growth expectations have stayed subdued," he said. "Buyback activity has stepped up and money has begun to flow into equity funds. Even intra-stock correlation has rebounded while sentiment is no longer complacent. Hence, the market should grind higher."
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Gauging the extent of sell in May, and watching laggards, likely will become key to dealing with the grind.
"What we have seen is the market, which was going through a bit of self-doubt if you will, has started to feel a little more confident about its prospects," said Sam Stovall, chief equity strategist at S&P Capital IQ.
Stovall said investors looking for an easy sell-in-May trade could be surprised.
"Whether it's simply an end-of-month knee-jerk reaction or the beginning of a don't-sell-in-May kind of move, we're seeing the cyclical sectors take leadership," he added. "We have to wait and see whether it's simply a knee-jerk reaction."