The TransGo A1-LU-BST Boost Valve for your 2001-2004 GM 6.6L Duramax Allison Transmission controls fluid flow to the converter clutch and reduces main line pressure from 255 PSI to 155 PSI when the converter clutch applies. In the LB7 transmission, the TransGo A1-LU-BST valve allows the amount of cut-back to be controlled so that mainline stays at up to 190 PSI.