If you have another ride pull one of the plugs out and take it with you to the parts store and match it up. That way you know you get the right kind for now then you can buy a little time to find out for sure what you have. Maybe post a picture of the engine?
2006 Chevy 2500 duramax - Tow Pig Stolen 10/15
New Tow Rig - '11 D-Max 3500 SRW CC 4x4
Our Jeep: '12 JKU Sport 4" RC lift, XD wheels, Cooper Discoverer ST tires