My 2000 Chevy Silverado 4.3 is stuttering when it rains out. What could be the cause?

[paintcode]

Whenever it rains outside or is slightly wet my truck seems to stutter, like its running out of gas, even when i have a full tank. Also for some reason when I am going up an incline like a hill or an up ramp it runs fine and when i go downward it seems worse. The truck is a 5 speed and it acts this way in every gear. Anybody have any ideas what is causing this?

 

[dathinman8]

I would check the spark plug wires. They get old and the insulation breaks down and the wires degrade. Wet conditions cause the wires to arc and you'll notice a definite miss. It could also be the cap and rotor for the same reasons. When you replace the wires make sure the coil terminals are clean and have no corrosion on them. Use Di-electric grease on the spark plug wire boots to prevent corrosion and moisture.