1993 gmc sierra

when ever it gest wet outside my sierra starts to misfire and bog down i think it is a sencer because i replaced the sparkplugs, wires, altnator, distributer, fule filter , and chip in the truck and it still mis fires and bogs down when it is damp or wet outside how can i fix the problem i bought the truck because it is old enouf to work on and new enouf to not have to mess whith a carborator