Welcome to GTP!
To fix your problem, go into the settings on GT3(in game), and just change the auto setup, and your gears should appear in normal form, and the car should drive normal...
If you have special settings with the hybrid program in the car's .ini file, then simply change it to - infront of the gear ratios, cause the program uses the opposite value, so - turns into +, and you coulda left out the - making it a negative value, and negative ratios propell the car in reverse.
That should help!