HELP - Tucking Below G/S ???

Recently all of my FS 2004 aircraft tuck below the G/S on an ILS approach. The aircraft intercepts OK but after the OM they start slowly going below and if left alone the aircraft will hit the ground prior to the runway. It's as though the ground is below the scenery ground being displayed! Can anyone explain how to correct this?

To stay on the ILS glideslope in Fltsim. you must control your speed.
In the 737 get N1 to about 48 or 50 % This should keep you on G/S.
In the Prop planes adjust the throttle as req'd.

with A/P on app will it auto fly it to the runway? I assume I turn altitude hold off and it will follow the glide slope? I use the GPS to vector to finals, and then wehn I am on 10 mile final I will switch over to NAV for the ILS approach. It keeps me on line pefrect its just not following the dang glide slope. I have to control power?