+1 on Giants. Very good bang for the buck. Out of curiosity, why are you set on a 29er?

Focus on the fit and ride of the bike, above componentry. A lot of that can be upgraded over time as lesser parts wear out. As for shifting as you go uphill, part of that is technique. Ideally, you shift while at the same time briefly letting up pressure on the pedals. My guess is that you were shifting under load. Not even the nicest drivetrains like that.