(Reuters) - Fiat Chrysler Automobiles <FCHA.MI> <FCAU.N> said on Tuesday it had revised more than five years of monthly U.S. vehicle sales figures to reflect a new reporting method, amid an investigation by federal authorities into claims of inflated sales figures.

FCA stopped short of admitting any wrongdoing and said it was not correcting past sales reports, but adjusting its internal practices to avoid miscalculations and better account for sales.

The company has boasted for several years of carving out year-over-year sales gains every month since April 2010, for a 75-month streak through June. But it said that winning streak would have ended nearly three years ago under the reporting methodology it is now adopting.

The maker of Jeep and Dodge vehicles said earlier this month that it was cooperating with investigations by the U.S. Justice Department and the Securities and Exchange Commission.

The probes, including a criminal investigation, stem from claims by some dealers that they were forced by Fiat Chrysler officials to falsify sales reports.

In its statement on Tuesday, the company said monthly U.S. sales reports in the past have had no impact on its reported revenue or financial statements issued quarterly.

FCA, like other major U.S. automakers, books revenue when vehicles are sold wholesale to dealers, not when sales are made to retail customers.

"Annual sales volumes under the new methodology for each year in the 2011-2016 period are within approximately 0.7 percent of the annual unit sales volumes previously reported," FCA's statement said.

One of the key changes is that the company will streamline the way its reports "fleet" sales each month to be at time of delivery from FCA. In the past, FCA says now, arbitrary measurements of sales to some fleet customers were made, often when a vehicle was being tailored after the factory sale to meet customer specifications.

An internal review at Fiat Chrysler has found that its U.S. sales figures were inflated by 5,000 to 6,000 vehicles, Automotive News reported on Monday, citing company sources. The report did not specify the time period.

U.S. 2015 FCA vehicle sales was restated to 2,257,641, up 0.6 percent from the figure initially reported.

FCA issued a table that shows its U.S. monthly auto sales since 2011 under the new and former counting method. http://origin-qps.onstreammedia.com/origin/multivu_archive/PRNA/ENR/FCA-US-Sales.pdf

The table shows that in some months sales would have been higher and in other months lower than they were initially reported by FCA.

(Reporting by Shashwat Awasthi in Bengaluru and Bernie Woodall in Detroit; Editing by Savio D'Souza and Tom Brown)