I have a 2001 Porsche Boxster (manual transmission). It will maintain speed as long as their is sufficient torque to do so in the current gear (or engine brakin

I have a 2001 Porsche Boxster (manual transmission). It will maintain speed as long as their is sufficient torque to do so in the current gear (or engine braking depending on uphill or down hill). Is it possible that you don't have much excess engine power at highway cruising speed and the car is only slowly responding to change in incline?