Santoli: Record-breaking rally may be overheating

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When a market that's spent more than a year in the red finally breaks to a fresh all-time high, it's not just a fluke.

The major indexes made dozens of approaches of their May 2015 records and declined every excuse to surmount them, so the current upside breach should at least be respected.

And the rally, which has lifted the and the Dow Jones industrial average to previously unseen heights, appears pretty sturdy: The vast majority of stocks are participating, credit markets are supportive and the longer-term trend has turned up.

Still, the ascent has been so steep that even believers in the breakout should be watchful for signs that this leg of the rally is growing overheated or fatigued.