Corvette servo vs tune line pressure - which firms shifts better?

Here is what the documentation says. Each point links to its source; details depend on your exact computer, harness and transmission.

• Holley's transmission tuning manual cautions that reducing commanded line pressure too much can quickly wear or damage the transmission. (Documents)
• In Holley's line-pressure tables a lower PWM duty cycle commands higher pressure, and 0 percent duty cycle gives maximum commanded pressure. (Documents)
• Holley warns that line-pressure values above roughly 40 to 50 percent duty cycle can produce inadequate pressure and risk transmission damage. (Documents)
• Holley's line-pressure curves are separately editable for gears 1 through 4, using TPS as the load axis for naturally aspirated/nitrous calibrations and MAP for turbo/supercharged calibrations. (Documents)
• In the EZ-TCU, the shift-firmness setting adjusts base line pressure; a higher number means higher pressure and firmer shifts, and pressure automatically increases with throttle so it is always maxed at full throttle. (Static)
• On a PCM-controlled 4L60E all parameters governing fluid pressures, shift-point RPM, and TCC operation stay under PCM control; a mechanical shift-improver kit firms shifts without changing PCM shift-point or pressure calibrations. (Documents)
• CompuShift arrives preprogrammed with base shift and line-pressure tables and built-in diagnostics, with shift points and line pressure adjustable for the application. (Phoenixtrans)

Confirm against the instructions for your exact parts before wiring. More: Transmission control in our tuning guide.