I would say #1 If the car is tuned perfect you would not be asking why it is not running correctly
#2 Best thing to do in times like this is to put the engine back to factory settings and the remote back center on sterring and throttle. Then once it is running really rich, tune it from there.
To me it sounds like your low end is way to lean. If it stalls when you let it idle. If it stalls while you let off gas top end may be too lean. After you put it to factory setting see if you can idle with out stalling. If you can then your low end is fine. Then I would make sure you do not lean out the top end too much.
Make sure you watch those setting. Leaning out an engine too much is very dangerous. Too Lean means not enough Nitro into the engine, not enough Nitro means not enough oil. Not enough oil means LOCK up. Then you will be buying a new engine.