I'm not sure what would cause this....I warm up the truck for about 5 minutes and then get it and turn my lights on, the RPM'S drop as if a huge load was applied to the electrical system it's really weird because lights all the way off it idles fine. Turn the markers on and it has a slight drop. Turn the lights on and it is a big drop. Has to be some kind of a load but I'm not sure where to begin. I recently blocked off my egr stuff after installing a header. Don't think it's connected to this issue though....any ideas?

 

Was it happenening before the EGR removal?

Turning the lights on, on a weak Alt can cause the RPMs to drop.

 

Check battery terminals, I had this problem when I did my emissions delete. Could also be a bad ground, alt could be going out, check the simple things before throwing a boat load of money at it.

 

Perfect! That gives me a great place to start. If I remember right, it was happening before the egr removal but very minimal. I've only had the truck since October so I'm not sure of the maintenance history. I'll get to work! Thanks guys!