Watch these S&P 500 levels to see if this rally has legs, says Art Cashin

Stock watcher Art Cashin said Tuesday the market is churning in a narrow band of resistance, one day after warning stock gains could be approaching stall speed.

The Dow, S&P 500, and Nasdaq closed at record highs on Monday, repeating a 21st-century feat first achieved last week, as stocks continue to grind higher.

But the new highs came on low volume, and the S&P topped out at 2,193.8 intraday. That was within the band of 2,191 to 2,194 Cashin identified as the resistance range.

"We churned through that band for virtually the whole day. By informal trader folklore, that band is still there, but you notch it up a little bit, so it becomes 2,192 to 2,195. We'll see if any rally takes us up there," Cashin, UBS' director of floor operations at the New York Stock Exchange, told CNBC's "Squawk on the Street."

On Tuesday, the S&P pulled back slightly to trade at about 2,182.

A four-day rally in crude markets should help stocks, Cashin said, but he added that top oil exporter Saudi Arabia is unlikely to dial back production much. Crude's rise has been driven by speculation that OPEC members and Russia could soon take action to prop up prices.

He also acknowledged the view that crude oil buying is primarily due to bears covering their short positions.

"It's a repeated fact. We've done it again and again and again, but we'll have to wait until that kind of slows down," he said.

Strategists and portfolio managers on Tuesday expressed little confidence that the good times in stock markets will keep rolling.

"It's really a classic 'meltup' with low growth, very little earnings vitality or revenue growth within the S&P," Stifel Nicolaus Portfolio Manager Chad Morganlander told CNBC's "Worldwide Exchange."

That meltup — or a sharp move higher driven by investors who don't want to miss out on gains — is common in August, Morganlander said. But he expects investors to return to reality next month, at which point deceleration in economic growth and underwhelming corporate earnings will come back into focus.

Expectations for earnings and revenue growth over the next 12 months now look "lofty," Morganlander said. Eventually, concern about earnings and stock valuations, as well as the likelihood the Federal Reserve will raise interest rates after the presidential election, could sap momentum from the markets, he said.

"I wouldn't be surprised to see somewhat of a sell-off over the course of the next six months," he said.

"I'm not saying its going to be a dramatic sell-off, but there's going to be a slight deceleration there."

Samantha Azzarello, global market strategist at JPMorgan Funds, said her firm has grown more cautious in the past six months ago.

JPMorgan Funds previously advised clients to stay in the market and expect low returns and higher volatility, but it now believes investors must be more tactical and perhaps avoid broad market exposure, Azzarello told CNBC's "Squawk Box."

Accommodative central bank policy continues to drive stock gains, she noted. The fact that easy money policy provided enough steam for the S&P to creep up to nearly 2,200 is "surprising," she added.

"While central banks are supportive in the medium term, in the longer run, we need to see fundamentals come back online," she said. Those fundamentals are underpinned by subdued but consistent U.S. economic growth and corporate earnings, which appear to have bottomed in the first quarter, she added.

Ed Keon, portfolio manager at investment strategy firm QMA, said his firm is also less bullish and more tactical these days. QMA is periodically taking profits on stock gains and growing less optimistic about second half corporate earnings, Keon said.

Still, he said stock market gains of 6 or 7 percent are not bad in the current low-growth, low-inflation world in which bonds are yielding just 1 or 2 percent.

"This is still a bull market, but it's an old bull market," he told "Squawk Box."