Do you have experienced pilots around to give it a test flight as well? It might be worth it.

It's hard from your description, but it sounds to me like a classic "leap off the ground and stall" type take off. The plane is leaving the ground too soon with out enough airspeed. One most RC models, the power-to-weight is just enough to climb nearly vertical to about the height you mention before gravity out does the motor and down comes the plane. Since you are stalled, up elevator is making it worse, not better. The old "up elevator makes you go up. Lots of up elevator makes you go down" thing.

Try taking a really long and fast take off run, and go easy on the elevator. when the plane leaves the ground, be ready to give a little down elevator to keep the climb as shallow as you can manage to avoid hitting anything. Do your first couple of turns with as shallow of a bank as you can manage, nice smooth and open, no bank-and-yank stuff.

There's a good chance that your elevator is too sensitive as well, so maybe turn down the rates there a little bit. I also agree with Truncator that you should double check the wing incidence, as it will make everything else worse.