My voltage drops and lights dim when I step on the accelerate only when first start the truck doesn't do it anymore once it warms up replaced alt. Batteries aren't old checked grounds changed battery temp sensor please help

 

When first started the voltage is set lower by the computer until the grid heaters turn off this will happens every time the truck is started.

 

OK will my volts go down when I step on the gas it comes back up when I let off