According to Trek's website, that bike had a pretty decent crankset on it (M442 Octalink). Are you saying you are rounding out the cranks where they interface with the bottom bracket? That seems highly suspect to me. I wonder if the bottom bracket is somehow faulty? How in the world did you break a cassette? You're a big guy, but I hardly think you are that big to destroy parts that easily inside of three months? By my calculations, based on the milage estimates you gave, you have no more than 1000 miles on that bike. Something isn't right here. I think I would be calling bull***** with the dealer.

Mark