A growing number of borrowers with auto loans are failing to make their monthly payments, according to a new report from Experian.

The credit reporting firm, which tracks millions of auto loans, said the percentage of auto loans delinquent for more than 60 days inched up in the fourth quarter to 0.78 percent from 0.76 percent the year before.

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"The percentage of delinquencies has trended upward within the last few years," said Melinda Zabritski, senior director of automotive financial solutions for Experian. "But it is worth noting, the percentages are still well below the high-water mark set in 2009."

While the delinquency rate is well below the historical average, economists say the uptick adds to concerns Americans may be showing signs of struggling financially. Earlier this month, a report by the Federal Reserve Bank of New York found more than 7 million borrowers were at least three months behind on their auto loans at the end of last year — more troubled borrowers than at the end of 2010 when overall delinquency rates were at their worst. The delinquency rates are lower now because the market for auto loans has since grown.

Zabritski says the data is worth watching, but not yet to the point of serious concern. "It's only natural to see an uptick in automotive delinquent loan volume. It's important to view these trends within the larger industry context," she said.

Americans are borrowing more money than ever to buy new vehicles: $1.17 billion in the fourth quarter, according to Experian. That's not surprising, given that consumers are buying more pickups and SUVs, which carry a higher sticker price than sedans.

The automotive web site Edmunds said the average transaction price for a new vehicle, what consumers actually paid dealers, in December hit an all-time high of $37,260, an increase of $6,598 compared with the same time in 2010. As a result of the higher prices, the average new vehicle auto loan in the fourth quarter climbed more than $600 to $31,722, according to Experian.

Not only are consumers borrowing more to pay for a new car or truck, they are also making higher monthly loan payments. Experian says the average monthly payment for a new vehicle hit a record high of $545, up $30 compared to a year ago. That increase is driving up interest in used vehicles that sell at a far lower price and typically carry a lower monthly payment.

Experian says the average used vehicle loan in the fourth quarter topped $20,000 for the first time ever, with the average used car having a monthly loan payment of $387.