Sprint's network has been undergoing a major reconstruction in the last year or so, but there are still some problems to be ironed out. Suspiciously, it has been Sprint's policy this whole time to pretend that the super-slow 1xRTT network doesn't exist. Instead, its devices just display 3G like everything is okay. The new Nexus 5 is apparently playing ball with Sprint too – if you're in a 1x zone, the phone will still read 3G.
There is a code commit for the Nexus 5 (Hammerhead) that specifically makes the change to show 3G for both EvDo Rev A (which can realistically be called 3G) and 1xRTT.
hammerhead: Show 1/2G networks as 3G for sprint In case of sprint and related-MVNO, the 3G icon displays for both Ev-DO Rev. A and 1xRTT.
So, if that 3G connection on Sprint is seeming a little sluggish on the Nexus 5, maybe you're not really on the network you think you are. 1xRTT has a realistic upper limit of 100kbps, which is a little slower than GSM 2G EDGE. It's bizarre that Google would make this sort of deceptive change, but they have been close with Sprint in recent years.
We reached out to Google and LG employees who made the commit to see if they can give us the lowdown on Sprint's rationale for hiding the 1x icon from users. I feel like it would just make people think that the 3G network is worse than it is. Though, if you don't pay attention to speed, you might think you have more 3G data than you really do. Shady business.
Update: While it's accurate 1xRTT is a 3G technology, it's pretty misleading to start calling it as such on the consumer side. It's not what they expect.