Try to find away to carry stuff without the backpack, like maybe a pack over the back fender. Backpacks are fine for running errands and commuting, but get tiring and burdensome on long rides. Others may disagree, but my days of wearing a backpack full of crap ended when I left the Marines.
Getting the bike fully broken in helps too. By fully broken in I mean like maybe even couple thousand miles. I would say my bikes feels better than it ever has with about 4k miles on the clock and a few services under its belt.