Shuts off and will not restart

Driving then will not restart. Also, it is hesitating when you accelerate have to press pedal maybe half way then starts bogging down, let up on petal then again press half way. At around thirty to thirty five mph it behaves better. But stop and may not restart. I have gone through the alarm problem no start changed ignition switch fixed that, also changed fuel pump. Do not know if flooding or starving of gas. Seems many have had same problem on 2000 Chevrolet's but I have not found the fix yet (help). Thanks. More, no start cranks restarts after sitting. Twice pressed on valve on rail test fuel and lots or pressure gas feels hot did this ten or so times then tried to start each time finally it restarted. Does seem to be getting hotter faster than before but it is now summer in Las Vegas.