OP
Adapter housing gasket is a possibility. Even the pan gasket could be, even with tight bolts some still leak for whatever reason. If the trans is overful then you could be seeing something from the breather but that usually runs down the side. The only other thing back there to cause your leak would be a cracked rear housing. You don't want that.
I would clean everything good like you did and see if it will leave a puddle for you. Then dont move the truck and find where it is . It seems like the rear of the pan is a "catch all" for anything leaking further forward like a spin on or front seal when driving.
Cold fluid check isn't very accurate, get the gauge up then run it through gears and check hot running.
I would try to isolate it before driving to your builder to save you both the hassle if possible. If its the rear housing gasket and you aren't comfortable then you'll be making a trip there. They are not bad to replace but you do not want to do one in the truck really, best to remove it so gravity is on your side.
His post literally says where the transfer case and transmssion leak. Same as mine, may be a totally different solution but we are both leaking fluid
originally yes, but his issue is further forward. Sounds like yours could be the gasket between t case and trans. Pump rub kit comes with a new one. Its a piece of cake. Drain case first, then Support trans with a jack. Then remove crossmember. 18mm to remove the bolts and nuts holding it to frame, 15mm if you have to remove an L bracket and 15mm for trans mount. Remove rear driveshaft with 11mm. Remove front driveshaft with 11mm. You will need prybar to hold front driveshaft unless using impact. You will also need to cut the oetiker clamp on the boot for the front shaft so it will slide out. Then unplug and unclip the wiring harness from the case as well as remove the vent hose. Undo shifting linkage from t case, then from trans to get it out of your way. Next you will need to lower the trans down some so you can reach the top nut holding the t case in. There are 6 nuts total, you will need a 15mm to remove them. An S or half moon ratcheting wrench makes life easy. Next put your drain pan under the joint to transmission, then lift up rear of t case to break seal and drain fluid. Now jack trans back up some if you haven't already. You remove case down through drivers side of truck, rotate the front shaft portion down a bit and let the trans flange nose dive and out of the truck it will come. The rest merchant has good instructions for.
If yours is actually spraying everywhere it could be a cracked rear housing but those are usually further forward than you describe.