I bought a used 2007 56cm trek1000. My height is 5'8 and I rock a short torso/long legs combo. I should be riding a 54cm, but it was a good deal ($200, good condition). As a result, my lower back hurts and I think it's b/c I'm over-stretching/over-reaching. I've read that getting a shorter stem will minimize my problem, but I'm not sure what I should get. I have a small budget and little experience so I was wondering if you guys could point me in the right direction as to what I should get. Thanks!