General Electric Capital Corp. came in second place with negative growth at 6.12%. Other banks such as U.S Bancorp., Fifth Third Bancorp., Suntrust Banks Inc., BMW Bank of North America and State Farm Bank BSB also experienced negative growth from the fourth quarter of 2012 to March 31, according to SNL Financial.

Meanwhile, credit unions are still in the midst of record auto loan growth. The latest data from CUNA Mutual Group's Credit Union Trends Report showed a 7.5% annual gain stemming from positive contributions from both new and used vehicle portfolios. At $183.5 billion vehicle loans represented 29.5% of all loans in April, but accounted for almost 42% of all credit union loan growth since April 2012.

Most of the recent strength is attributable to the new vehicle portfolio, up 8.7% year-over-year and 2.7% year to date, said Dave Colby, chief economist at CUNA Mutual.

"One key reason for this renewed strength is that competition from subsidized financing has pulled-back as new light vehicle sales have strengthened," Colby noted.

The new vehicle loan rate at credit unions is now 3.27% and the used rate is 3.91%. Colby said both rates continue to decline and like March, are down roughly 50 basis points from their prior year level.

SNL Financial said of the 100 largest depository auto lenders, 43 were banks or thrifts, while 57 were credit unions as of March 31.

Indeed, credit unions are ­holding their own against some of the country's biggest auto lenders. The $5 billion Navy Federal Credit Union in Vienna, Va., said $2.3 billion of its record $3.1 billion in consumer loan originations so far in 2013 are from auto loans.

Higher member optimism about their personal finances and the economy helped Navy Federal book $753 million in consumer loan originations in May–the best month in the cooperative's 80-year history, according to the credit union.

Navy Federal Corporate Economist Alan MacEachin points to two key factors regarding the credit union's record year-to-date in auto loan originations – including $527 million in May: historically low interest rates and the average age of vehicles in the U.S. at greater than 11 years.

"Major automakers reported significant sales increases in May compared to last year, further demonstrating that consumers are taking advantage of low rates and replacing older vehicles," said MacEachin.

According to Navy Federal, there's also mounting evidence that consumers may be overcoming this year's federal spending cuts and the expiration of the payroll tax cut.

While consumer confidence indices are still below their pre-recession peaks, MacEachin said they currently stand at their highest levels in several years.

"An improving job market, stabilizing-to-increasing real estate values, and surging stocks are creating a greater sense of wealth and confidence among U.S. consumers," MacEachin said. "These positive trends bode well for increased consumer spending and stronger economic growth."