U.S. automakers are coming off their best year for sales in five years, helped by extremely low interest rates that have encouraged more borrowing.Analysts expect credit card debt to stay weak this year. That could slow consumer spending and keep growth weak. One reason is that Americans will have smaller paychecks. Congress and the White House reached an agreement last month to prevent income taxes from rising on most Americans. But the deal did not extend a temporary cut in Social Security taxes, which expired on Jan. 1. The two percentage point increase means a person earning $50,000 a year will have about $1,000 less to spend in 2013. A household with two high-paid workers will have up to $4,500 less. Most economists expect the tax increase could trim the economy's growth by about one-half a percentage point this year. Consumers spent more in December, according to a government report last week, though the increase was slower than in November. Consumer spending drives about 70 percent of the economy. The overall economy actually shrank in the October-December period, dipping at an annual rate of 0.1 percent. It was the first quarterly decline since the recession was ending in the summer of 2009. The Federal Reserve's borrowing report covers auto loans, student loans and credit cards. It excludes mortgages, home equity loans and other loans tied to real estate.