Idle Problems

So I recently noticed that at stop signs/red lights etc, when Im in drive and stopped, my RPMs dip down from about 1000 to 500 and I almost feel liek im goign to stall. It jsut kinda bounces back and fourth. It doesnt do it in neutral though. Ive had some trany prolems recently with lazy shifting so Im wondering if theres a commonality. Perhaps torque converter or something? Im also throwing a SES light now, which i need to get checked to see what code it is. I just re did headers cats ad exhaust within the pastcouple months, so i wonder if its related to that. If anyone has any light they can shed please do.

97 k1500 350

If the SES light is on, get the codes pulled and post back. Autozone does it for free.

//2000CAYukon

Sorry for the delay... code was for a cylinder misfire

Back when I installed my headers I had miswired my sparkplugs and switched up 2 cylinders, 1 and 3 i believe, and drove to college with it (3 hours trip) so at this point im assuming i fried those spark plugs. Figured Ide check with you guys first though to make sure i dont spend money in places i dont need to. Thanks in advance.

JCarr

Also, how exactly does the excessive heat from the new headers affect my wires. Will I see visual damage (ie. melting) or not? Thanks.