Slow mobile data after 5.1 update

So I updated my phone a month ago to 5.1 from 5.0.2. Via ota update. Ever since then my mobile data is just sooo slow, pretty much unusable. I have to use WiFi everywhere I go. When I was on 5.0.2 I had no problens could stream videos in full HD with any lag and do Web page searche. so about a week ago I did a fresh install, wiped everything and did the latest us custom firmware, but still no change. I thiught I saw a thread on this issue but I I can not find it and tried googleing and doing the forum search but no luck😢 I hoping some one can get me in the right direction or throw some ideas to a fix. Please