I had the same issue (I posted a thread in this forum called Mis-Shift).
I have purchased the B&M shifter but have not had time to install it. I can tell you 2 things that really help with shifting this car:
1. Thumb down on 3-4, 5-6 shifts. I would also like to add that if you give it a slight nudge to the right as your headed to 4th, it really helps. Just a VERY slight nudge to ensure its going in the right direction.
2. Relax, and concentrate on what your doing. I think this is the biggest part of driving this car period. With so many other cars (Sports and exotics included), you can jump and and drive with very aggressive inputs, but the car will stay planted. With the Viper you have to smooth your inputs out (throttle, gearchange, clutch, steering), to keep the car planted. I noted that I would mis-shift when I was gunning it, and everything is happening so fast that I end up YANKING the shifter straight down from 3rd, and end up buzzing 2nd. Now when I drive this car, I think about exactly what I'm doing, and I don't get too excited. This allows me to not ****** the wheel, or stomp the throttle or yank the shifter.
Best wishes to you, and be safe!