I have a new Cannondale Syapse Carbon 2, front ultegra, compact crank, rear dura-ace, 12-25 cassette. No matter how much I adjust the front derailleur, to the point it rubs even when on the third largest rear cog, when I shift onto the largest rear cog and pedal hard the chain slips off the front. The LBS is baffled. Because of the suspect origin of the bike (too long a story) there is no warranty. Please help!