ok, just got an email from TSW:
The solution that we are aware of for this issue is to use a free
program called JoyToKey (you can google it), which lets you map your
shifter's buttons to keyboard keys, then map those key presses to your
in-game shifting function.
This double shifting behavior is a combination of the delay time in the
game's shift detection, and the way the firmware on our shifter chips
works with Windows 7 or possibly just with 64bit OS. This issue doesn't
occur with windows XP (only tested 32bit) no matter the game, but we've
had some reports and have confirmed it ourselves on 64 bit win7, on
those games which don't have a built-in or adjustable shift delay.
We've planned to address this by working on a new firmware version but
have not had the opportunity to do so yet, nor has it been a top
priority since the issue can be addressed as described with a simple fix
for those few who've experienced it.
Im gonna try it and report
great customer service from TSW, and the shifter is AWESOME..