Did you get a whole new TX/RX pair or just the 6ch receiver? The 4ch transmitters may be quite different inside even though they look identical.

I have about 5 Dumbos and they're all over the place in quality. I could also never get channels 3-5 to work right. Your problem could be a crappy receiver or your switch could have burned out.

They also have a lot of weird modes and very unclear instructions, you could have ended up in tank mode (making ch3 a throttle channel?), or drift mode, or who knows, while trying to turn on the gyro.