Before assuming head gaskets, thoroughly check everything else out. There is a tube going from the back of the water pump back to the oil cooler area. Mine was not leaking but since I was doing injectors, head gaskets, water pump etc., I decided to pull the tube and replace the o ring. Big mistake as when we re-installed the tube, we cut the o ring. We got everything back together, started it up and the water just poured out! We had to pull the water pump and loosen the motor mount to get the new o ring in without cutting it again. Being that the leak appears to be at the pan gasket area, it could very well be this tube/o ring thats leaking.....
Coolant lines across the top of the engine can leak also, with the water running back along the valley and down the back of the head surface. On my leaking head gasket, it was very obvious when under the truck looking up at the rear head mating surface that it was leaking at the mating surface itself and not water coming down the valley.
Head gaskets are a B$tch to do, rule everything else out first!
2001 CC/LB/2wd, Modded stock air box, 4" MagnaFlow exhaust, Replaced at 147K: injectors, head gaskets, water pump, CP3. Mike L Stage III tranny with ML converter and valve body, EFI Live by Trent Nell, 285/75/16's on Eagle rims, 6" RCD lift kit with about 3" removed!