That could very well be Network Vision. Service got terrible for me a couple weeks ago (NW Chicago suburbs). I was struggling to get 300Kb/s, usually getting around 100 (and this is at 3:30am). I had been getting a solid 300-400Kb/s before that. I don't really remember how long the terrible speeds lasted, but a couple days after one test, I was suddenly getting 1.0-1.4Mb/s in the exact same spot at the same time.
Now, I'm noticing that my data disconnects when I get to specific places as I'm driving. According to S4GRU, that is because the new equipment that they're using is not compatible with the old equipment. So, the upgraded towers (where I'm now getting great speeds) can't hand off the signal to the towers with older equipment. Instead, the phone holds onto the signal from the upgraded tower as long as it can, until which time you are completely disconnected from the network, and your phone has to connect to the legacy towers itself.
Hang in there. It will all be over soon. Then, we will all get to enjoy the LTE goodness Sprint has waiting for us. Plus, after Network Vision is complete, Sprint won't have to overhaul its network on this scale ever again (theoretically). It will be upgradable via nothing more than a software upgrade and an expansion of backhaul bandwidth, for which Sprint is already prepared.