Place called Mopar part USA has had some of the cheapest parts, yes oem, I've found and at times I've had to pay no shipping charges. Bought my UC springs there.
Heater Core (oem) at Mopar Part USA $181.25
2004 GC Spec. Edit. V8 4x4 Quadra-Trac II. Bright Silver Metallic Clear Coat, 4" lift, RE shocks, adj. JKS CAs all around, 265/75/16, ProtoFab winch bumper, Vortex 10,000 lb. winch, dual OME steering stabilizer, Rockyroad rockrails, skids, JKS Discos. Addco front & rear sway bar, & Aussie locker.