In 1987-9, computers of the age were more than capable of getting the math and physics right on flight simulation. Graphics fidelity was another matter :)
It is perfectly ordinary for pilots to be all over the map with airspeed and descent rate as you did. They may be trying to get enough airspeed across the prop to attempt a "windmill start". They may be tuning for best glide. They may be slewing or otherwise deliberately scrubbing off energy in order to arrive at the target landing site with enough energy but not too much.
In fixed-wing aircraft, energy is stored in two forms: airspeed (kinetic) and altitude (potential). Flight is all about trading one for another, and there's nothing magic about the trade - you can't create more energy than you had, nor destroy it merely by trading. Although... I hear some airplanes have an "engine" that can add new energy :)
This energy arbitrage was exactly what you were doing, and that's what it's all about.
If you arrive at the runway stripes with too much energy, you will either be too fast or too high in the sky.
Anyway, if you arrive at the runway threshold with too much energy, you will either be going too fast, or too high in the sky. And you could find yourself in an "impossible turn" situation where your surplus is not enough to get lined up on a runway before you run out of energy.
So whatever you were doing to get on the ground, it was working :)