How can I run longer without cramps?

Well I do go out to run, but sometimes take a power walking break, and then start running again. I hate side stitches and cramps! I want to be able to run for a full hour without getting them. It just seems I jog, sprint, power walk, repeat. Also, want to know the best way to land with the foot so there is less impact. I land mid foot and then roll up to my toes. By the way, I’m almost 6 ft. I would like to be able to do 10k’s.