My '95 Infiniti G20 with over 200K miles is redlining while I'm doing only about 45 mph! What does this mean?

Eventually it shifts down to between 2K and 4K RPMs. It seems this is happening after it shifts back down to the first gear after I've slowed down and I'm climbing a hill.

I'm not a car expert. I just know it shouldn't be acting the way it is. Just want to know how serious this could be.

The transmission is not shifting the way it should. Take it to a reputable transmission shop.

it would probably be cheaper to get a new transmission all together rather than repair that one. just a thought