Hi, in need of an assist here. I bought a new set of Mavic Ksyrium SL wheels. Installed a new Ultegra 6700 12/25 cassette. Put new Vittoria Rubino Pro tires on. On 3 test rides totalling about 90 miles, it is very obvious that it is taking much more effort for significantly reduced performace than usual. Took wheel to LBS. Bearings and internal components OK. Only thing noted was that cassette does not spin as freely on new Mvic hub as my cassette spins on my prior set of wheels. Switched wheel sets to old set. Avg speed about 20 mph, max speed 29-32 range. Switched back to Mavics, average speed over same course 17-18.5 , max speeds around 25 ish. Checked brakes, not an issue. Questions: Could new tires be adding this much rolling restistance?? Could new cassette be this stiff to cause this? When I ride the Mavics I feel like someone is sitting on the back of my bike. Had heard nothing but great things about them and am very perplexed right now. WTH? Any thoughts??