Sorry to hear of your issues, but it's a little consoling to hear, as I've had the same thing since returning from overseas yesterday. I wondered if I had confused the phone with using an overseas SIM card on my trip. Sounds like something else is going on.
Without wifi (which works just fine), I can only get data when set to CDMA. Changing to CDMA/LTE or Automatic immediately shuts data off. I'm in central VA, where I believe there are NO plans for LTE conversion. (Not sure if the other network upgrades are happening.) Interestingly, according to the app Signal Check, when my phone network settings are CDMA/LTE or Automatic, it says my connection is 1xRTT/eHRPD on nTelos (a regional "partner" of Sprint, I believe). When on CDMA only, it says 1xRTT/EV-DO on nTelos/Carrier Unknown. Prior to leaving on vacation, I did not have these issues, and the carrier was always listed as Sprint. Seems like there's been some shifting around of the partner(s) providing the bandwidth.
Update: After reading some on s4gru, I've come to realize that I'm stuck in a corporate limbo area. Shentel to the west has upgraded to LTE like mad around Harrisonburg and north, but Sprint and nTelos are doing some BS corporate dance that's delaying upgrades here. Bummer. I did see that eHRPD is a theoretically better version of EVDO that allows for smoother handoffs to LTE, but that's of little comfort given that LTE is not in the near future.
UPDATE #2: Just before my overseas trip, Sprint Customer Care sent an update to my phone, and I think she may have disabled 4G. This evening, I called again and another reset fixed my issue. Seems like at least some of my corporate cynicism was ill-founded. Signal Check says I'm back on Sprint EV-DO Rev A (but I'm away from home again).