I've made the 'lemme drop just 5 lbs. before this trip' mistake one too many times. Been miserable and bonking on the very first day, and never felt strong the entire trip.
If anything, watch the calories NOW, then ramp back up well before the ride. Instead of a true diet, just eat clean until the ride - nothing fried, nothing with cream sauce, easy on the cheese, nothing white - rice, bread, or potatoes, but whole wheat, brown rice and sweet potatoes. Obviously, no sugary stuff. While you might eat the same calories as before, try to make sure all the calories HELP your health, not hinder.