The quickest fix might be to change your gearing if the hills are getting to you. Either get a smaller chainring or a larger rear cog.

Your position on the bike also has something to do with it. The Windsor has upright Northroads style handlebars, right? That riding position can wear you out quickly as it doesn't give you much leverage climbing. Try picking up an old Cro-Mo steel roadbike on craigslist to see if you like the difference.