My normal driving mode is S/M 6 with ECT set to PWR. Lots of hills around me as well, I just shift up or down as required (or, just leave it at 6 if I'm lazy). FYI, if cruise control is set, it stays on in 4, 5 and 6 - if you shift down to 3, then it shuts off.
HTH
Thanks for explaining. I'll also set the ECT to PWR tomorrow to see if that makes a difference.
Cheers!