(FORTUNE Magazine) – Economists have only one thing on their minds this summer (professionally speaking, that is): Has the economy really slowed? If so, Federal Reserve Chairman Alan Greenspan can loosen his chokehold on short-term rates, business can resume booming, and the stock market can go back to making us all rich. If not, Greenspan will have to keep tightening--and that means the business climate and capital markets will probably have to get worse before they can get better.

The standard, American Economic Association-approved way to answer such pressing questions is to Consult the Data. But the data on this issue are contradictory: One month new-home sales tumble and the next they soar, while other indicators, like consumer confidence, remain at record levels. Besides, economic figures describe what happened one to three months ago. That's not much help here. Economists are pretty sure that the GDP numbers that come out at the end of July will show that the economy cooled in the second quarter, but what happens after that is anybody's guess. "A lingering question is whether the data capture what's going on right now," says John Lipsky, chief economist at Chase Manhattan Bank. "We've had eye-popping strength in the first quarter, and we're expecting weakness in the second, but what we don't know is whether that will be sustained."

Rather than wait to find out, we decided to see for ourselves by visiting the economy's frontlines. (Andy Serwer takes a similar approach in his column on page 329.) The place we chose to look was Denver, because the Mile High City and places like it (such as Phoenix, Dallas, and Atlanta) are the heart of the economic expansion. Denver is a key player in the tech boom (especially telecom), a major hub for trucking, and a magnet for educated, affluent workers. "Unless economies like Denver's stop barreling along," says Mark Zandi, RFA Dismal Sciences chief economist, "the Fed won't have finished raising rates."

Stand in the middle of downtown Denver, and it quickly becomes clear that barreling along is still the order of the day. Construction cranes and HELP WANTED signs are as common as Rockies baseball caps. The 16th Street mall, quiet as a Trappist monastery as recently as four years ago, is abuzz with shoppers. Chic loft apartments, ultramodern office buildings, and a new football stadium rise from muddy work sites. Once-seedy lower downtown has been reborn as the swank, restaurant- and art-gallery-encrusted "Lodo" district. And Denver's vast airport swarms with business travelers--the bleary-eyed byproducts of an economy operating at maximum warp speed.

Digging deeper into Denver's economic boom, we visited a Re/Max real estate agency in the suburb of Highlands Ranch. Homebuyers are highly sensitive to interest rates, so if the economy is slowing, it should show up first in the housing market. And what better time than now: In the past year mortgage rates have risen from around 6.75% to around 8.25%.

Someone apparently forgot to tell Paula and Cliff Davis, however. We accompanied the retired schoolteachers on a house hunt with Re/Max agents (and father and son) Jerry and Steve McGuire and found the Davises' consumer confidence utterly unshaken.

The first house the Davises visited was a gray ranch-style with four bedrooms and a good-sized kitchen for $350,000. No sale: The garage didn't have room for their Lexus, their Chevy Blazer, and their antique 1959 MGA roadster. Their second stop was a $324,000 two-story contemporary with plenty of garage space in a new development called Castle Pines North. Again, thanks but no thanks: Castle Pines North is too far south for the Davises' needs. Oddly enough, mortgage rates never even come up for discussion. "We just want to find the right house," says Paula.

While the Davises strike us as surprisingly price-insensitive, Jerry McGuire, a 27-year veteran of Denver's housing market, says they're tightwads compared with the buyers of six months ago, who'd snap up a shack on the freeway if it were listed. Today's shoppers are more discerning. And in June, for the first time in a while, the number of houses on sale increased from the previous month, while those under contract decreased. If that combination recurs in future months, it could suggest that supply is starting to catch up with demand and that the market is losing momentum.

At first glance, the Denver hub of Swift Transportation, the nation's third-largest trucking group, is another sign that things are slowing down. The company's vast terminal is empty but for a handful of 18-wheelers lined up to refuel and a few idle drivers loitering on the steps of the main office building.

Up in the dispatch center--the half-dozen office cubicles that make up the nerve center of Swift's Denver operation--a different picture emerges. Operations manager Wayne Whitney, better known as "Doc," shouts frenetically into three phones at once, trying to match Swift's 225 trucks and drivers with customers and destinations. When one truck lumbers into Denver to drop its freight, Doc matches it with an outbound load, sometimes within hours. In other words, the emptiness of the terminal yard didn't mean there was nothing going on at Swift. Quite the contrary: It meant that almost the entire fleet was out hauling goods.

Swift's trucks mainly move consumer goods bound for Target Stores, Sears, J.C. Penney, Wal-Mart, and other mass merchandisers, which makes Swift's business a good proxy for retail demand. The more consumers spend, the more Swift carries. And there is a lot to carry these days. In the past five years Swift has had to more than double the size of its fleet to meet demand. In a slowdown, says CFO Bill Riley, the company would cut back on the number of vehicles it deploys. But for now Riley is content with 225 trucks--an indication that activity may have reached a plateau, but at a record high level. "Retailers around the country are expecting a strong second half, and so are we," says Riley. He believes that revenues, which grew 20% through June, will pop another 20% before December.

It's the same story at Webb Interactive Services, over in trendy Lodo. Webb is an Internet infrastructure services company whose products help small businesses increase Internet usage. CEO Perry Evans, 40, says demand is so strong that Webb had to go to work even before its building was completed. Software engineers and programmers spent the first days in their new digs dodging plumbers connecting a sprinkler system overhead.

Since Webb's customers are small businesses, which tend to react quickly to changes in consumer demand, Evans would be among the first to sense a slowdown. If one were to happen, his customers would stop asking for products that handle growth and look more for applications that help reduce costs. "It's a subtle change," he explains, "but we're not seeing any concern yet about slowing growth." There's certainly no concern at Webb itself, by the way. In the past year the company has gone from 40 employees to 100. Evans plans to hire another 30 by the end of the year and estimates that he'll hire four a month for the foreseeable future thereafter.

What's the verdict? While you can find some signs in real estate and trucking that we've hit a plateau, it's hard to imagine a real slowdown occurring here without Greenspan's help. The expansion has been good to Denver, and its people just keep spending. In Denver--and across the country--uninhibited consumer spending radiates through the economy like a powerful electric current.

The message from Denver is clear: If Greenspan is serious about slowing consumer spending, he's not finished yet. He'll raise rates in August and at least once more.