It seems that the OP, Trek and the dealer are all agreed that it's a frame stiffness problem. If so, and if all the OP wants are suggestions for stiffer frames, I can't help him, though I'm sure there are others here who might.
OTOH- Based on the tiny bit of info provided so far, I'm skeptical that a stiffer frame will change anything. At this point I'm forced to wonder if this is a case of taking Pepto-Bismol for a headache.
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