If were my RC, I would set the needles back to the factory / break-in settings and retune it. If that doesn't help, you may have other problems.
It might sound kind of silly, but if you ran the engine too lean for that gallon of fuel, you may have worn it out. When the p/s is worn, it will do like you said. It will run great while it's cold. When it gets warm, the sleeve expands and there is room for air to leak around the piston. The reduces performace and can cause it to just die.
Here are a couple of way's I've learned to test for piston / sleeve wear.
1.) try and turn the flywheel by hand (with the glow plug installed). When you get to top dead center (tdc), it should become really hard to turn. If you push really hard, you should be able to turn it over, but it shouldn't be easy. If it turns over easy, you need an engine rebuild.
2.) since this is a stadium truck, you can do the pullstart test. put the rc on the ground and see if you can pick the rc up by the pullstart cord (with the glow plug installed). if the engine turns over and the cord spools out, the piston and sleeve are worn. I tight piston and sleeve will cause the car to lift in the air by the pullstart cord.
3.) remove the glow plug and turn the engine by hand via the flywheel. When you get close to top dead center (tdc), you should feel a "pinch" where the sleeve constricts around the piston. no pinch - no compression - time for rebuild.
4.) remove the engine (glow plug installed). hold the engine by the flywheel and put the engine close to top dead center. Then postion the head so that it's pointed at an angle, being held up by the engine compression. When you hold the engine in this way by the flywheel, it should be able to support it's weight for 3-4 seconds before flipping over TDC.
that's more information that you probably needed, but it will be here the next time someone else needs it.
