Right so this is basically what we call a Alien Big Cat sighting, and we get them constantly over here in the UK - Cheshire's had quite a few reports over the years actually. The Beast of Bodmin, the Fen Tiger, loads of documented cases. Point being, large melanistic cats turning up in places they shouldn't exist is way more common than people realise globally.
What you're describing sounds like it could be a melanistic bobcat that's significantly larger than normal, or honestly a mountain lion that's been misidentified as black due to low light conditions. Melanistic mountain lions are technically unconfirmed but the sightings never really stop.
One thing I'd ask - did you get any photos? Even bad ones are worth analysing. The gait pattern tells you a lot more than the colour does. A big domestic cat moves completely differently to a genuine wild felid and that difference shows up even in blurry footage.
Also roughly what county in Tennessee, and was it daylight or dusk? Details matter enormously with these reports.