Alright, update as of 8/6/13:
I have not been using my browsers (Chrome and Dolphin Browser) to access the YouTube mobile site, but I went ahead and cleared the cache on both anyway. I restarted my phone after doing so. I encountered some buffering issues this morning so I tested things outside. I had the same buffering issues as previous when I was streaming an HD video (after about 3 minutes), and similar, though less pronounced, buffering issues when streaming the same video in SD (after about 7 minutes, buffered for less time and only once or twice per minute). My signal strength when outdoors was -76 to -78 dBm, 62 to 63 asu.