Put a little bit of oil UV dye in your crankcase and get a small UV light. (both of these can be purchased on ebay for like 5 bucks). Degrease your engine and drive around for about 20 minutes.
Shine the UV light on the engine, when it's dark, and you will see where the leak is coming from.
05 GC Limited - 4.7 Quadra-Trac II ~127,000 miles
12 GC Limited - 5.7 V8 Quadra-Drive II ~11,000 miles
99 GC Limited - 4.7 V8 - Quadra Drive (sold; 110,000 miles)
02 GC Laredo - I6 - Selec Trac (sold; 123,000 miles)
04 GC Limited - 4.7 V8 - Quadra Drive (sold; 132,000 miles)
07 GC Limited - 4.7 V8 - Quadra-Trac II (sold; 78,000 miles)