The "always upshift at" places an absolute engine RPM limit on each gear. The controller will always upshift when this engine RPM is reached. The controller measures engine speed from the tachometer input, if connected, or calculates engine speed based on driveshaft speed and gear ratio. The tachometer is the more accurate measurement because all torque converters slip.

As the "shift speed", adjustment is increased, the transmission shifts at greater speeds for a given throttle position. The "always upshift at" provides a cap for this adjustment. This allows you to have the transmission shift at high RPM with light throttle, but still not exceed the engine's RPM limit at full throttle.