It's likely that a lot more consumers are using tablets to shop for new vehicles. Are automakers ready? The second wave of J.D. Power and Associates' samiannual study on the effectiveness manufacturer websites finds that they are certainly heading that way. J.D. Power finds that 35% of new-car shoppers own tablets versus 21% in January. The Westlake Village, Calif.-based market research firm also reports that overall satisfaction with automakers' websites is up largely because the manufacturers have retooled their consumer web sites to be more platform agnostic and generally easier to use.  The firm's semiannual Manufacturer Website Evaluation Study, which J.D. Power has been doing for 13 years, uses four criteria to measure…