Had an alternator problem and it tested bad, so we put another on....within a week the dash volt meter was erratic....sometimes it'd show 19 volts, at other times it'd show 9 volts, at other times it'd show 13.5 volts...... Well, took that alternator back and at the parts store it tested bad..... so we got another, and had it tested there before I left and it tested good...... put it on, started the engine and it was showing 10.7 volts..... I put my diagnostic scanner and ran Operational Data and it showed 10.7 volts as well...... what next should I try??