Wild black snake sighted

[Bogertophis]

I live in Eastern TN in the Appalachian mountains.
... brown rat snake? (I couldn’t find it on native snake list but I’ve caught a 60-70 inch brown snake in the wood before and was told it’s a brown rat snake)...

The only rat snake that I can think of that's brown (actually patterned with brown & grey) is a Great Plains rat snake, aka Pantherophis emoryi, aka Emory's rat snake, but I don't think it's range covers your area. I wonder what you've seen? You might ask your local (state) dept. of Fish & Game. I suspect it was a black rat snake with enough red undertones (some have none & others have a lot of red) so that it appeared brown rather than black? Because the size you describe doesn't fit an Emory's rat snake either- they're smaller.