This also interested me because I have the boomba trans adapter and I sometime get stuck going to 3rd from 2nd. Might just be me not shifting properly. But I also have the Cobb rmm
After you installed it, did you complete the cable adjustment procedure? If not, it's fairly simple after you get the air box, battery and batt tray out.
Set the parking brake.
Put the car in neutral.
Release the yellow clip on the black cable. (Be careful here, the yellow clip should NOT come off).
You won't be popping the cable off the pin, but make sure the cable moves freely.
Put the car in 4th gear. The cable should now be locked.
Before you take the car out of 4th gear, push the clip back in.
Now, you're good to go.