1500 / 2500 / 3500 545RFE Transmission 2003, High Performance Automatic Transmission Line Pressure Booster Kit (RFE-LB1) by Sonnax. Includes: Pressure Regulator Spring, Wiring Harness with Connectors. Sonnax line pressure booster kit is an improved design over a simple resistor circuit. Featuring an integrated chip circuit and a stronger pressure regulator spring, this new kit delivers 10 psi increase at lower pressure range and 25 psi increase at higher pressure ranges. These kits provide progressive pressure increase which gives you smooth engagements and lower load on the pump at idle, but a greater increase in pressure as the transmission is worked harder.