I seem to have a slight electrical problem. When I start my truck and when it can idle the dial says "13" volts. AS soon as I start driving and get on the freeway my voltage slowly starts to decrease. As I cruz the voltage drops to "8" volts and in the red zone. Then when I get off the freeway and stopped at a red light my voltage increases. I have been tracking the pattern of the voltage fluctuation for about two weeks and this is the characteristics of it. Some times the dial decrease to the lowest registered setting. I am afraid that the truck might die. Each day the voltage dips lower and lower. Could this be a problem with my ignition system? There seems to be a short somewhere, obviously, but it seems to be "RPM" or "speed" dependent. Any feed back would be great for trying to solve my problem. I know this is a vague description of my problem, but maybe some pointers where to start looking. Thanks.