I got a problem.
 

Alright guys i've got an 01 silverado 5.3 ecsb. I just recently started having a problem that happens only when it rains and what happens is it idles really low and shakes the truck and when I cruise at about 45 it surges really bad. When i get into 55 or 65 it still surges but not as bad and if I decelerate or accelerate it still surges but is significatly less. I checked all my vaccum lines, spark plugs, wires, and coil pack, and I checked my fuel pressure and everything is fine. I've never had this problem before and dont know of anyone else having it so I need some advice.

I would probably post this over at performancetrucks.net