If you have the 4.8/5.3/6.0 engine, then its most certainly NOT the intake gasket, because these engines use a "dry" intake (no coolant goes through the intake).
If your getting coolant in the oil, then you may have a bad oil cooler (if equipped) or a bad cylinder head (common with these cylinder heads). To verify if its the head, fill the cooling system full (no air pockets) and then pressurize the cooling system. Remove the valve covers (both) and let sit for 5 minutes. Then inspect around the middle row of head bolts (between the rockers). if you see coolant puddle on top of the standing oil, the heads are porous.