I have a 1996 Jetta 2.0 liter 4-Cylinder Manual. I know this car was built back when the fastest speed limit in America was 55, so I'd like to know if it's normal for this car to run at 4k RPMs while going 70mph in 5th-gear? If it is normal, is it safe to be doing this for nearly 100 miles?

 

No it's not normal it sounds like you have the wrong fifth gears in your O2O
I bought a replacement trans that had this problem

And yes you can drive at 4k rpms for over an hour with no problem

 

What would be a normal RPM if my car were using the correct gear-ratio?

 

I'm guessing because I just had my waterpump go out so I can't test it but I wanna say closer to 3k

In 4th the tach needle should mimic the speedo needle
In fifth the speedo needle should be farther clockwise than the tach