When you remove the thermostat outlet; make sure that it's surface is perfectly flat. If necessary, sand flat on a sheet of glass using wet/dry sandpaper.
Use a little RTV sealant on the new gasket. I like to raise the passenger side of the truck to hold the thermostat in place by gravity as I install the outlet pipe. Don't overtighten either. Coolant level after this? You know the program.
Turns out a clamp got loose. Go figure. Haha I felt around the bottom edge of the hose and felt the coolant so I tightened the clamp and it hasn't been leaking!
Update. I've found another leak. This ones worse than the hose that got loose. Idk what it is exactly but I can describe it for now. Will get a couple pics up.
So for the evidence, under the carb is pretty wet. With coolant. The coolant drips from the back of the oil pan onto the ground. I checked the hose again and it's still tight. Ono sign of it leaking from the thermostat. The pipe that the bypass hose goes to is pretty damp too. Everything under that is wet. Doesn't look like it's coming from the hoses near the firewall neither.
And there are three coolant bypass hoses, don't overlook those. One is at the front of the engine, U-shaped, easy to see. The other two are pretty hidden on the passenger side of the engine.