Coolant overflow bubbles over, but... not head gasket?

In my previous thread, I bought a 2006 tundra with 298k miles on it with a broken timing belt. I put a new timing kit on it and have been driving the truck around. Here's the new issue..
Every time I go somewhere and get out of the truck, I smell coolant. There's no coolant on the pavement or on the engine, nor any coolant coming out of the exhaust. I think, the smell is coming from the overflow, and if I drive it prolonged periods of time, 20+ minutes, The overflow will.. overflow, and slowly leak out the overflow. So, I thought.. crap, headgasket is blown. I did a pressure test, and it will not hold pressure. I took the intake manifold off, replaced an O ring in the tube that goes under the intake to the rear of the engine, and it holds pressure a little better, but still leaks down in 30 seconds. I do not see coolant ANYWHERE though, so figured its a headgasket for sure. I checked in the cylinders, checked under the vehicle, checked the freeze plugs, checked each connection, nothing is leaking, nothing is seeping, no coolant visible anywhere.
I bought one of those kits on Amazon and performed the test to check for combustion gases in the coolant. The truck ran for 20 minutes, and I revved the engine up to 3000 rpms several times for a minute each time. The test came back no combustion gases present. It stayed blue, the same exact color I started with. In that time, the coolant in the overflow tank went up about 1/2-3/4 inch.

Every time I start the truck, it starts right up, no smoke, no coolant smell.

What is the deal? Why is my system building pressure but no coolant gasses present? I'm going to run the test again tomorrow, but am mystified as to what is going on. I might go get a dye kit from Autozone and put that in the coolant and check it with a black light, but I'm at a loss as to where this coolant is going, why my system is pressurizing, yet, no gas present in the coolant.

 

Pressure test the radiator cap?

 

I was thinking I would go buy a new rad cap tomorrow, but the pressure tester I used clamps down right where the rad cap goes and it still leaked. Maybe there's a small crack in the top of the radiator neck or something, but I sprayed soapy wooter on everything around there and found no bubbles coming from anywhere when I pumped the pressure up.

 

Might get a new thermostat and be sure to put jiggle valve up at 12:00 position. Post some pics of radiator, hoses and crossover pipe areas.

 

Heater core?