If you use manual trim at all, it turns combat trim off for you, so yes, you should be able to trim manually without combat trim. It's the only possible way to trim.
Something is goofy with your setup. If you are in auto climb mode, you should be able to do the following:
1. auto climb to 5000 feet
2. turn off your engine
3. let the aircraft stabilize in a glide with a consistent rate of descent
4. turn off combat trim
The airplane should keep the autopilot trim setting and stay in a constant rate of descent in a fairly trim state.
If you have auto takeoff set, launch, but cancel takeoff by jiggling the stick. Look at your trim settings and rudder at least should be hard over. Turn off combat trim and check if they jump. If they do, your setup isn't right.
Look at your key map to see what's mapped to the autopilot functions. Perhaps you're using Trim Set instead of combat trim toggle?
