@Jmacg: Other users with multiple ISP's have confirmed TCL YouTube streaming performance is worse. @Technies response proves that TCL-specific DNS settings do affect performance.
@Technie: Thanks for your post. I tested the alternative DNS settings & found YouTube improved (at times by a lot, at other times by a little). As Freitasm and yourself mentioned above, Facebook goes from perfect, to barely operational when using the public DNS setting. Look forward to seeing your helpdesk ticket updates.
@Freitasm: This issue has been occurring for longer than a month.
Idle on-topic observation: My limited Youtube use over the last couple of days has been somewhat improved. Still in wait-and-see mode however.
I hate you.