Not flaming or bashing you, but you should try and provide a little more information about the kit that you are running. Providing more information will allow others to quickly provide you some avenues to pursue for answers/solutions.
Is the kit you have an RTR? (ready to run kit that comes with radio and receiver)
How new is the kit? Is it brand new or been sitting on shelf for a few months?
Is the radio a 2.4 Ghz radio or an older FM radio?
I will suggest you do the following to help narrow down the problem:
1. Replace all batteries in the transmitter with fresh batteries. If you have a rechargeable battery pack, make sure it is fully charged. Also check the contacts in the transmitter where the batteries go, make sure there is no corrosion on the contacts. If there is, clean them with rubbing alcohol and an old tooth brush (firm bristles).
2. Check the antenna on the transmitter for any anomalies like kinks, looseness or obvious damage. Fix those issues if you can.
3. Check the antenna on the receiver for cuts, nicks, bends or other damage. The receiver antenna can be prone to damage depending on where it is installed in the vehicle.
3. Check the routing of the receivers antenna. If it is near the speed controller/motor, it may be experiencing interference. When I say near, I mean like attached to it or within a few millimeters of those components. If it is, re-route the antenna. If you do have an older FM style receiver, and the antenna looks like it has been "trimmed/shortened", then thats the reason for the decreased reception. The receiver antenna will need to be replaced or the whole receiver if you are not confident in replacing the antenna.
4. If the antenna is running along any carbon fiber chassis parts, it can cause interference. Provide some clearance from these components also.
5. If all this does not fix your issue, then you may need to replace your transmitter and/or receiver.
Ready to Run kits typically use inferior/cheap electronics in order to keep costs low for the buyer, unfortunately you lose performance.
If you have an older FM style radio, I would seriously consider upgrading to a newer 2.4 Ghz style radio. They are more reliable and other hobbyists cannot jam/take over your car by using the same frequency your radio/receiver is using.
Good luck, I hope you can figure out the issue.