Could this be the problem?

[Espeefan]

Yes, a cut antenna on the reciever will reduce the range of the model. Perhaps more then you would think. Glitching would be the first sign. How does the model run with the radio a couple feet from the model? If it's okay then, step away and see what it does. A lot of these antennas are specific lenghts, determined by the frequency and channel.

Other things that can cause a lot of glitching include a motor without capacitors on it (to reduce the electrical noise they produce), an antenna wrapped around something metal, or resting on aluminum, an antenna wrapped tightly around itself, and high or low frequency vibrations within the model, caused usually by a nitro powered 2 stroke engine (probably not the case here).

I would start with getting the proper length antenna on the receiver first. You can always coil the excess around an antenna tube, and then bend the tube so it fits under the body and is hidden. That keeps the scale look, and retains the functionality of the model.