Excellent, barrykai--sometimes small tweaks help lots. Me personally, if I mash the pedals too hard early in the ride or stand too much to climb, the cramps hit me in the 40-45 mile range also. If I concentrate on a faster cadence/lower gear and avoid mashing/standing during climbs I'll usually finish 50-60 milers without pains. So try a faster rpm in lower gears and I'll bet you'll notice a difference.