So I have a problem on a 92 silverado 5.7 with 270k miles on it and I'm in need of some advise..

The truck runs and drives great from the start no problem starting has full power durring acceleration runs perfectly fine until I drive it for about 10 miles or so when it gets warmed up it looses all power durring acceleration almost like it isn't advancing the timing it stumbles like it isn't getting fuel but I have put a brand new fuel pump in it but I can put it in neutral going down the road. And shut it off and then start it back up and it runs like I just started it full power no stumbling on acceleration transmission kicks down to passing gear like normal then after another 10 miles or so it. Go's back to loosing all power but as long as I shut it off and start it back up when it starts doing it Its like nothing is wrong with it... But the longer i drive it the more often it happens.

I have replaces the battery, the distributer, the coil, the fuel pump, plugs and wires, the electronics spark controls module, set the timing just as the manual says to, just about everthing I can think of to do with timing. All vacuum lines are hooked up and everthing is connected properly... I haven't replaced the map sensor yet or the knock sensor but I am at a loss has anyone ever had this problem?? If so what did you do to fix it its about to drive me crazy throwing money at it with no difference in what is going on can anyone share some insight on this problem if they know of it or have had their truck do the same thing and what did you do to fix the problem.. Thanks guys I really appreciate any help I can get!!!!
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