Where are you and what is your service area. I'm in NYC my 3g speeds are acceptable, not great/ not bad,but it consistent at least.
Sprint has the slowest 3g speeds of the big four carriers. I think it is because they let everyone and anyone piggyback off their network to run mvno's. Boost and virgin are the major ones but there is also some third party companies running mvno's off f sprints 3g network. I think that has a lot to do with the bogged downed speeds.