Before completely removing the intercooler for cleaning, you should just check and see if there's any oil residue on the inlets and outlet by popping off the hot side and cold side tubes. If you do see oil residue, then you may want to go ahead and clean out the intercooler. The best way is to just remove it from the truck, hose it out, and then run warm water and a mild soap (Dawn or Simple Green) through it. Then shake it out and let it dry for a bit before reinstallation.