Hey there antman808,welcome to ONEDERLAND!
Got my T-MOBILE branded ONE a day after you.Have't had any performance issues whatsoever w/my handset,but,others may & your issue probably isn't linked to being of a certain carrier.
Admittedly,this area is something I'm not going to be of much help,as I stream most of my media & my phone is relatively empty/lotsa storage space available.(BTW,no problems streaming video or audio,regardless of data connection).
It'll get a bit busier here later in the day & the photogs in the crowd will be along to assist in troubleshooting.
I hope that aside from this,you're thoroughly enjoying the ONE.