how do you know for certain its not related to the signal? you can still get signal quality issues even with full strength.
could be related to growing pains with the LTE network--which is still a work in progress country - wide.
contact sprint, give them your zip code and see if there are any signal issues in your area. Taking the phone into a corporate service center so they can test the radio is also a good idea.
if you are rooted, then you could have other issues related to the ROM. You may want to post this in the rooting section as well.