U.S. homeowners are getting better about keeping up with their mortgage payments, driving the percentage of borrowers who have fallen behind to a three-year low, according to a new report. Still, the rate of decline remains slow, credit reporting agency TransUnion said Wednesday. The percentage of mortgages going unpaid is unlikely to return anytime soon to where it was before the housing market crashed. Some 5.49 percent of the nation's mortgage holders were behind on their payments by 60 days or more in the April-to-June period, the agency said. That's the lowest level since the first quarter of 2009. The second-quarter delinquency rate is down from 5.82 percent in the same period last year, and below the 5.78 percent rate for the first three months of 2012. The positive second-quarter trend coincided with an improving outlook for the U.S. housing market.