Sounds like you went out of radio range... how far was it? Were you using good batteries in the recievers/transmitter?
Buy yourself a couple of failsafes, they really save you from events like you describe, or if nothing else, wire up a throttle return spring strong enough to bring the throttle back to idle(or brake would be best) if you lose radio signal.
Lots of different things can mess up AM radios mostly metal on metal contact though, so if you're near a chain link fence or something similar, that it could be messing with your radio signal.
GJ to the guys who said you bought a pos instead of actually helping with the issues you're having.
If you really want to get different trucks, get your money back and goto a LHS (or at least talk to a hobby store in your country) about getting trucks they stock parts for, doesnt matter what you buy you're going to break things, all of these trucks are big, heavy and powerful, parts will break
Btw the failsafe(s) thing is good plan whether or not you plan on keeping the warheads.