certain it's a turkey vulture. No question.
I see those things constantly, probably at least 20 per day, 365 days a year. They are SO common anymore. Black vultures are getting that way too. I remember when I was a kid, seeing a black vulture was something to get excited about. Now they are like rats, everywhere you go.
Not even close to a red-tail or other true buteo.
Easiest way to tell a vulture and a hawk apart is the wing angle (dihedral). Soaring turkey vultures bring their wings back into a "V" ("V" for "vulture), while hawks soar with almost a flat wingspan. Another way to tell is the wings themselves. Turkey vultures' primary wing feathers are transparent white when viewed from beneath, while the "arms" are dark black (dunkerofbunker's pic clearly shows that). Hawks are all opaque, either white or brown typically.
As far as flying in groups, yes hawks will do that at times, especially on migrations or in breeding rituals, but vultures are much more likely to do that all the time.