Every couple of weeks I have done this same course on a dirt road, which has a 600 foot elevation gain. I started with 15 pounds, and today I carried 25 pounds of water up, in just under 30 minutes.
Next week I am going to move to a different course, with steeper, and rockier footing. The goal - from Steve House's, Training For The Uphill Athlete - is to build more muscular endurance. Who knows when, but I expect to be climbing in the Sierras sometime in the next couple of months.