It's completely Sprint's issue. They had some serious issues handling an influx of new customers a couple years ago, and the arrival of the iPhone has only made things worse. Meanwhile, they wasted a ton of money barking up the wrong tree with WiMAX.
Do some google searches, tons of people with iPhones and android phones alike have super slow data. My own epic gets around 0.3 Mbps on 3g. The 4g in the twin cities is better than average, usually around 6 mbps. But I just switched to T-Mobile and now I get 10-12 mbps. I'm done with Sprint and their slow network.