There probably isn't anything wrong with your phone and you've probably done all you could to get the best possible speeds. I think speed is dependent on too many factors other than your phone such as your location, reception, movement, and the number of others utilizing the same site.
I live in the LA area and I've experienced speeds from 4 to 212 kbps. In my office, I generally get about 70 - 80. If I'm outdoors with full bars i average about 110. My speeds are anything but consistent.