dpcompt

If your driving up a 6-7% grade at 60mph, is it more efficient to stay in the high and rely on the turbo boost or downshift one or more gears and run with zero boost?

dgbaudiphile

Pretty confident it would be best to downshift - you're leveraging gearing vs engine output. Depending on your gear ratios, you should have more torque when downshiifting - at least when we're talking lower gears. It's gets close as you move up through the gears. In the end, the answer lies in where ever you get max torque.