Before you did your update your phone was recieving 1 band of 4GLte, with no problems. When you did your update, you gave your phone 2 more bands, 26 and 41, but what Sprint didn't tell you, was that we are haveing ECSFB issues in the Denver area when we go to use our Spark phones. All towers in our area have to get upgraded for us to use our new tri band phones on 4GLTE. Sprint is in the process of doing this right now. There is a thread in our group discussing it. Type ECSFB in the search engine at the top. Best wishes.
ecsfb thread