When it seems to run better with more data traffic it might be your phone switching between cells or protocols. Maybe this helps a little bit:
http://www.pocketables.com/2013/08/how-to-keep-your-android-conne cted-to-3g-on-a-fringe-coverage-area.html
Meo
http://www.pocketables.com/2013/08/how-to-keep-your-android-conne cted-to-3g-on-a-fringe-coverage-area.html
Meo