Modern transmissions in heavy-duty trucks like the Chevy 3500HD use much more sophisticated electronic control systems. Instead of A and B solenoids controlling basic shift functions, they employ multiple electronically controlled shift solenoids and pressure control valves managed by a sophisticated Transmission Control Module (TCM). These components work together to control clutch engagement and shifting throughout a wider range of gears and operating conditions. The specific number and function of these solenoids varies depending on the exact year and type of transmission (Allison, etc.).
