Transgo Allison 1000 Cut Back Valve.
For 2001, 2002, 2003, 2004 GM 6.6L Duramax LB7
This valve is the converter flow valve. This valve controls fluid to the converter clutch and cuts back pressure from 250 psi ( or so ) to 145 psi when the converter clutch applies. This valve will bring that pressure to a more acceptable 170-190 psi, and much more depending on application. This valve is very important in high horsepower applications to hold the most extreme conditions.