1995 Chevy Monte Carlo transmission fluid is black

It seems that you ATF is worn out! Have you ever serviced your transmission?
Normal transmission maintenance involves replacing the fluid and filter every 2 years/30,000 miles (sometime even sooner in extreme driving conditions).
Your fluid is probably not doing its lubrication job anymore, and if you keep driving your car you'll end up with bad transmission damage (it may already be the case).
Do a complete fluid exchange, and put a new transmission filter.
When you remove transmission pan, check at the bottom for debris. If you find big metal chunks or things like that, that's bad news.

Also, make sure your transmission cooler lines are not leaking or clogged. And check your fluid for coolant contamination which would indicate a leak in your ATF cooler inside your radiator.

The fact that your transmission runs a little hotter than normal on hills is normal, but if your fluid is worn out, it's killing your transmission.
Also, the hotter your transmission runs the sooner you have to service it.