Ford Bronco hard to start

Engine problem
Ford Bronco V8 Four Wheel Drive Manual 140000 miles

I have a 1976 bronco with a 302. It is hard to start. When warm. When it sits overnight, I get in, pump the gas 2 or 3 times, and it usually starts right up. However, sometimes when I am driving, it dies, like someone flipped a switch, and then it doesn't want to start. This morning I drove for 10 - 15 minutes with no problem, shut is off, came back out 30 minutes later and it wouldn't start. It took me 30 minutes of turning it over for 3 to 5 seconds, then letting it rest, then trying again. After I got it started, I drove for 5 minutes and it died, but then it started right up. I shut it off, went in the store for 15 minutes, when I came out it started, I drove for 1 or 2 minutes and it died again, then it took me 20 minutes to get it going. Then it made it all the way home, 10 Minutes (5 miles) without stopping. One thing I notice when the bronco is hard to start, it seems like the car doesn't even try to start until I am releasing the ignition. In other words, I turn the key to start the car, it turns the engine over but doesn't "really" try to start until I am releasing the ignition, just before the engine stops turning over, it tries to kick. Help!