I'm facing the same problem with my Giant Escape 3 and considering an upgrade to the drivetrain. I'm maxing out on some runs I do. Not saying I need a lot more but I sometimes find myself reaching for the shifter and finding nothing more there.

The Escape 3 has a Shimano TZ31 14x34, 7-speed freewheel cassette and Shimano M131, 28/38/48 crankset (note I pasted this from their specs, I don't know much about the drivetrain side of things yet!).