NEW YORK (AP) - Coming off of a weak back-to-school shopping period, a research firm expects holiday sales growth will be slower this year during the crucial holiday season. Shoppers are also expected to visit fewer stores as they research purchases online. Retail revenue in November and December should rise 2.4 percent during the biggest shopping period of the year, Chicago-based research firm ShopperTrak said Tuesday. That compares with a 3 percent increase in 2012 from 2011. While the job picture has been improving in the U.S. and the turnaround in the housing market is gaining traction, the improvements have not been enough to sustain higher levels of spending for most Americans. Most continue to juggle tepid wage gains with a higher cost of living.