Pull the transmission out of your back wheel, take it apart, clean all of the old grease and grim off of everything, put it back together with a new seal and gasket (Available from zippy) and new oil. Then clean and repack your front bearings. that will help you out a lot. drilling a couple of holes in your airbox and rejetting your carb will help some more. After that, you'll probably need a 64cc kit to get up to 35+. Check out the vespa performance in the wiki. Treats is supposed to be getting some more DR 64cc kits soon and they work great for the money.
I'm about 195. I have a grande and a ciao that are a little more souped up than that and they will both go 40 and climb hills no problem.