I see the GT ZuM has a flat bar. I second the suggestion to get a fitting session, and explore swapping the grips with ergonomic ones. In addition to changing the stem, your bars might be shortened so that the match the width of your shoulders better. Ergon makes very nice ergonomic grips (in two sizes, for small and large hands) -- the bar ends give you more hand positions while you ride. Search for them in Amazon.