I've been riding my new OCR2 for about a month now, and I haven't noticed many problems with the crankset (Truvativ Touro) until I started going on longer and longer rides. Last night I went on a 40KM ride with an avg speed of 25KMH and a max speed of 55KMH, and as I was looking at the largest chain ring on the crankset, I could see the ring oscillate towards and away from the derailleur, causing some chain rub, which I *really* don't like. Also, on some uphill sections, my chain just completely came off of the large chain ring in the front, which is odd, because chains usually get derailed in the rear! I suspect the crankset or BB, but the wonderful wrench at the LBS where I bought this bike claimed that chain rub was normal, and that there was nothing wrong with the crankset. What do you guys think might be wrong here?

FWIW: The bike is a size M, and I'm 175lbs @ ~5.11