I have a truck that the volt gauge flickers when it is started. The alternator was repalced twice and two different batteries. Also th whole grounding system was gone through. Now even the wipers work after the truck has been running for awhile not right away and when they start each time the brake light lights up. Also when the headlights are on you can see them flicker like a strob light. When I plow snow now the volt gauge goes all the way down to the bottom and even starves the fuel pump unless the switch is released. The plow was checked on my other truck and is not a problem.

I would go over the whole ignition system. Install new ACDelco spark plugs, spark plug wires, igniter, and coil. I would also replace the fuel filter and check the idle rpm. Your engine may be struggling so much to stay going that it's not doing a good job of handling the alternator and other demands placed on it. If these steps don't solve the problem, consider installing a remanufactured engine control computer.

I have went through all of that and the truck runs great. Actually I am a marine mechanic for 12 years so pretty good with motors.