11.5 lbs is a lot for a 60/90 size plane. Its no wonder it wants to snap out, especially at your elevation. Is the model nose heavy? Does the elevator (trimmed for flight) show some "up" trim? If so, you might see if you can reposition some weight for a more nuetral balance. 10mm travel doesn't sound like a lot, but it can still be too much. It is a warbird model and will likely have best results set to fly like a warbird.

One other thing, are you using an appropriate size fuel tank? A 10 oz (or even 8oz) is all you need for the DLE 20. No sense in hauling excess baggage in the form of extra fuel.

Good luck.