Sounds like you have the run and situps down. For pushups, try the following: after you do your chest lift day, finish with 3x20 pushups. If you can't do it, do as many as you can then go to your knees to finish. It sounds easy, but by forcing your body to learn how to do it after completing a full chest workout, you would be suprised how many pushups you can do when fresh.
BTW, I am a 100% pushup/situp guy and a 60% run. 260 FTW lol.