Hi,this is my first time posting and I apoligize in advance if I don't use the proper terminology. I got a trek 4300, new in 2002. I have used it off and on for short rides to work and short trail rides. I am female, 5'9" and large framed. I sometimes get frustrated with the shifting on my bike, especially the front and I'm not sure if it just needs a tune up. I did a little reading and it sounds like it may be weakness of the bike. Also, the bike is a little heavy for me, I have the 17.5" frame. Basically, I want something low maintenance that can get up some hills. I was thinking of an upgrade to a trek 6500 or 6700. I don't have disc brakes now, should I get them? Please help me, I am not mechanically inclined, but am very interested in advice. Thanks for your time!