i had a nasty vibration at highway speeds. i personally balanced the tires 3 different times. problem never went away. finally went to sullivan tire and had the tires roadforce balanced. cost me $40. best $40 i ever spent...no vibration up to 95 mph. may be higher as well, but didn't check!
2003 Ford Expedition: 5.4L, harley supercharger, 2.93 upper pulley, 4lb lower pulley, c&l plenum, jlp cai, LFP SBTB, FTSP, Magnaflow 3" catback, Eclipse AVN-5510, white face gauges, cobalt c2 boost gauge, ddm hid's, 379 rwhp, 465 rwtq sold 11/3/12
2009 Ford Flex Limited AWD