What year is year is your Viper? The '92s(first year)does not have the reverse lockout. Your lockout solenoid is probably defective. Be careful shifting to 5th until you replace it. There may be several owners driving around with this problem, and not realize it. To test the lockout, drive above 5 mph and try to shift into reverse(don't release the clutch pedal!). If it goes in reverse, or grinds, the lockout is not engaging. This happened to my '94. Good luck.