Agree with others who have said that changing bikes won't make you faster. My two cents:
- lighten the 30 lbs if you can. This is _definitely_ hurting you on the hills (you said you have hilly terrain).
- climb the hills faster. You lose more time on hills than descending. This could could consist of a combination of optimized gearing for your level of fitness, improved physical conditioning.
- optimize your bike fit. By this I mean changing handlebars to achieve a more aero position on the flats and better climbing leverage on the hills. Optimize how the cargo is being carried on the bicycle.