When I tested the Specialized tricross, the left Shimano shifter was definitely more of a pain to move. Besides biking, I'm also a pianist with a fairly strong death grip so I'm fairly certain it was not a matter of hand strength.

To the OP: glad the bike shop fixed it. Shifting shouldn't be a hassle and hand strength is only one contributing factor. Specialized and bike shop personnel should tinker with the components first instead of simply telling you to strengthen your hand.