There have been a couple of flights where I was told to go from 8000ft to 3500 feet in an ammount of time that was not possible for me to make the glide slope, or hit the runway for that matter. Would rebuilding the runways fix that issue? Is it a symptom of something else?

Rebuilding the RC scenery database using the latest makerwys (see pinned topic) should insure RC has the correct data as long as your scenery priority is set correctly and there are no duplication issues of the af tagged (afcad, afx, etc.) type files.

 

Frequently RC starts you down on the next step before you have reached the bottom altitude in your current step to maintain as far as possible a constant descent. Sometimes on straight in approaches RC may keep you too high.

 

Slow down your aircraft in the traffic pattern and use flaps to increase drag and increase the time you have for descent. It sounds like your problem is occurring after the fixed crossing restriction altitude as you enter the airport traffic area.

 

It is best to have charts for your STAR (if used) and especially the instrument approach. This will allow for proper approach planning. (I assume here you are talking about an airport with published approaches.)

 

Other than the crossing restriction you can also user the NOTAMS feature of RC to deviate from approach instructions without RC complaining. In that regard you accept all obstacle clearance responsibility when you deviate from the controller's instructions. A chart will provide minimum altitudes for the approach path you are using.