Id be surprised if this was really a radio issue, unless you were running on a 1000' diameter track.

Is your receiver antenna in good shape? Is it properly mounted and the antenna exposed properly. Batteries in the TX ok?

What exactly were the symptoms?

Obviously you can spend money on new tx - Airtronics, Futaba, etc. But many people get away with RTR radios at tracks all over the country, and these are not as good as what you have.