What kind of hills are you going up on the highway that you feel the need to downshift to be able to climb them?
My '12 V6 manual 2.73 car never had any issues with going uphill in 6th with the cruise set at 65.
And it would lug itself around town in 6th just fine down to 1000 rpm.
Bingo, same here. 40mph in town? drop that trans
into 6th. mine has no issues chugging along at 60-65 on the highway either. and I have some big hills on my commute