"They have better power, they are more reliable and they get better gas mileage" than their unleaded counterparts, he said.

But these days, with diesel hovering at nearly $4.80 per gallon, up sharply from about $3 per gallon a year ago, the market for them has all but evaporated.

"You used to be able to buy and sell them like crazy," he said. "But the gas prices are really freaking people out now."

Over the past two years, owners of diesel-powered vehicles have simply absorbed the rising cost of the fuel. But in recent months, many drivers have had enough, flooding the market with diesel-powered trucks and cars few want to buy. Scroll through several online car-selling sites and you have to sort through hundreds of listings before you find one that has actually been sold.

Jensen, of B. Jensen Auto Sales in Midvale, said he still has some success selling diesel trucks for about $6,000 or less, but he has to price the vehicles well below market value. His last sales of diesel trucks, for example, were for vehicles priced at only $3,200 and $2,500. "You get into the $10,000-to-$15,000-or-more range, and it can get extremely difficult" to find anyone willing to buy them.

Nationally, truck sales overall are down, prompting Ford to delay by several months its new F-150 design as dealers struggle to sell enough of the current model. GM said it has halted work on the next-generation Silverado and is placing more emphasis on car development.

There are a number of people who still need to drive a truck because they work in industries such as farming or construction that require the transport of equipment or heavy loads. But even those potential customers probably will be opting for more basic models instead of $45,000, fully loaded versions, said Joseph Phillippi of AutoTrends Consulting Inc.

Car dealers say that buyers who don't have to have a truck are seeking more fuel-efficient cars.

The problem for those trying to get out of a truck - especially a diesel powered-one - is reduced trade-in values.

That puts a lot of people "upside down" in their auto loans by owing more than their trucks are worth.

Tony Bailey of Roy worries he could be in that spot soon if he has to lower the price much more on his Dodge Ram diesel-powered pickup to get it sold. He already has taken $1,000 off the $15,000 he believes the truck is worth. He hasn't had much in the way of inquiries.

"Some people who own their cars outright can just keep dropping their prices," he said. "I can't do that without having to come up with a lot of money."

Bailey said he wants to start saving for the future - especially a home of his own - but that the high cost of diesel is making it hard.

"If I could afford it, I would keep it," but instead he's looking for a more fuel-efficient passenger car to commute between Roy and Layton.

Bailey bought his truck several years ago, when diesel prices were less expensive than unleaded. "When diesel prices hit $4, I thought, 'This is ridiculous.' But then it got worse."

The outlook for gasoline and diesel prices remains unclear. According to the Energy Information Administration, the price of diesel began to surpass the cost of unleaded gasoline in late 2004. Much of the problem has centered on the strong demand for diesel in China and emerging countries, with prices up nearly $2 a gallon in the past year and no ceiling in sight.

As prices climb toward $5 and some consumers steer clear of diesel-powered vehicles, there will always be those devoted diesel fans who will keep on trucking regardless of cost.

Manny Climent of American Fork, is one of those people. He bought his first diesel truck about two years ago, a time when he remembers filling up for $2.30 a gallon.

With prices double that today, he says he still loves the power of a diesel, so he shops around but usually "I just pay the price."

And he has also found himself paying in other ways. He recently bought a newer diesel-powered Dodge truck and has been a bit surprised at the lack of interest he's been getting while trying to sell the 2003 Ford F350 Lariat Super Duty he bought two years ago.

"It's got all the bells and whistles and it's worth more than $28,000." He's asking $20,700, but so far, no takers.

Climent said he isn't going to reduce his asking price much further. "I'm not going to give it away. If I can't sell it, I guess I'll just sit on it a while and see what happens."

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* GANNETT NEWS SERVICE contributed to this article.