Are you having trouble engaging reverse, or are you having the issue that the electronic reverse won't even come on (i.e. the little light doesn't come on and it's doesn't beep).
If it's the later I've discovered that if you start the engine without holding the start button down for a few seconds beforehand for the fuel pump to engage, then reverse should work fine. I've had to turn off the engine and restart it that way. I think that replacing the TPS or something can fix this but not enough of an issue for me yet. Mine is an 09 GT.
