Why does the battery light flicker every time I excelerate after motor is warm ? on 2000 Chevrolet S10

It starts like a champion every day. And I have replaced the battery , both battery cables , spark plugs , spark plug wires , distributor cap and rotor , yet as soon as the motor is at normal operating temperature I cannot drive any faster then 35 mph. I have to feather the throttle and put the hazard lights on. If and every time I accelerate even just a little the battery light starts flickering and the truck starts acting like a bucking bronco. Big loss of power and the battery light flickering like crazy. The only think that I have not replaced is the alternator. The craziest thing that happened recently was I was in gear coasting down a mountain around 50-55 mph and I was not touching the pedals and the battery light flickered a few times and I could feel a bump in the motors rythim. Does this clue to in at all as to what I need to replace to get this to stop happening ?

Asked by for the 2000 Chevrolet S10
The red battery light is blinking is that right? Do you have a gauge for the charging system? Ever have to jump start it? Any diagnostic testing been done? Any trouble codes? Fuel pressure readings engine running and engine off? SURE plug wires are not crossed up? Need more info.!
The voltmeter on the dash does not show any fluctuation. I have never had to jump start it. No trouble codes showing. Fuel pressure is fine and no wires are crossed. It starts beautifully and quick and strong every morning but then after it is warmed up when I give it throttle it bucks like its not getting any fuel but the battery light flashes every single time I give it gas. I think I am going to put an alternator in it. It is the only thing that I have not done. Maybe the alternator works fine when its cold and then when it gets extremely hot it starts malfunctioning.
Pickup with the 2.2 or 4.3? I know what's in the Blazers. This info. may help.
It has the 4.3 V6 Vortec motor.