i had the same issue.... signal rises, drops, 3G icons dissapears, appears again, and even goes into roaming for a moment... its because its contantly looking for signal where its not supposed to IMO (the whole WCDMA and >50% TWS issue)
what dramatically helped me with this issue is going to settings/ call settings/ system select/ and choose Sprint (its on Automatic by Default)
I have an issue where they are stealing copper from the antenna that feeds signal to my house and signal is HORRIBLE for the past month. Calls wont arrive, its a b*tch to make a call and have it actually connect, and internet is such a pain that it made me want to throw my device against the wall...
after i did that setting adjustment, my connections are much much better, its like the antenna is fine now... still testing