ORIGINAL: Jellyson
Cmdr. Bob, I don't think the weight would make that much difference--if you didn't change anything else, I would suspect that the gyro might be drawing more current than we would expect. First thing I'd try would be to unplug the gyro but leave it on the heli, wire up the tail like normal, and see if it still won't climb out.
Comander Bob
If for some reason you don't want to try what I suggest, of course that is entirely up to you.
It probably isn't what is wrong anyway.