If you're putting in lots of up elevator trim to fly it under power, then you're probably right: you've got too much down thrust. Mine flies straight and true with just a couple clicks of down elevator. Check out your thrust line and dial it in so you're not needing so much elevator trim. If you're comfortable flying it out of trim, dial the elevator back to neutral and see if it will fly better that way at idle. Could be scary since the plane can be jumpy if you've got lots of throw...