2003 3500 pushing coolant out overflow tube.

Hey guys, I recently got this van from a dealer and it turned out to be a lemon. After going into limp mode on the way home, and fixing that by replacing the MAF and cleaning the EGR, I got a low coolant warning light. I filled it up but it got low again when I was driving on the freeway. Then I read up on the forum and read about the possibility of needing a new head gasket. I did notice that there is some pressure release when the radiator cap is removed days after driving it, accompanied with gargling. I tested to see if the coolant was coming out of the overflow by duck taping a pastic bottle to the overflow tube and I filled the whole thing up after 25 minutes on the freeway. So it seems like my head gasket is screwed, but it just seems strange cause the van only has 107K. Basically I'm asking for a second opinion from you guys. Also the heat only works intermittently. And it's not overheating. Could a bad thermostat cause this? I don't want to just tear into a motor for no good reason. Should I bother replacing my radiator cap?

I guess a stuck thermostat could do that, or bad water pump.
But test for head gasket leak is oil in coolant or brown mayo in oil, on oil cap. If not those then I'd suspect thermostat

These engines do have a failure point on the head gasket that only allows combustion gasses to enter the coolant system, and not affect the oil. So the lack of mayo in the oil is not a good indication.

It definitely sounds like a head gasket leak. And mileage doesn't really come into it, it can happen on a single overheating event which could be caused by anything.

The cooling system diagnostic chart suggests that air trapped in the cooling system could cause your symptoms. Was the coolant replaced recently? The "Standard Procedure" for refilling warns that air could be trapped unless the procedure is followed carefully. I've seen this failure to "bleed" the system in other vehicles.

STANDARD PROCEDURE - REFILLING COOLING SYSTEM (1) Tighten the radiator drain and the cylinder block drain plug(s) (if removed). Tighten the engine drain plug to 22 lbs. ft. (30 N·m) (2) Fill system using a 50/50 mixture of ethyleneglycol antifreeze and low mineral content water. Fill radiator to top and add sufficient coolant to the coolant recovery pressure container to raise level to COLD MINIMUM mark. (3) With heater control unit in the HEAT position, operate engine with container cap in place. (4) After engine has reached normal operating temperature, shut engine off and allow it to cool. When engine is cooling down, coolant will be drawn into the radiator from the pressure container. (5) Add coolant to pressure container as necessary. Only add coolant to the container when the engine is cold. Coolant level in a warm engine will be higher due to thermal expansion. To purge the cooling system of all air, this heat up/cool down cycle (adding coolant to cold engine) must be performed three times. Add necessary coolant to raise container level to the COLD MINIMUM mark after each cool down period.

Trapped air on its own won't cause cold pressurising of the system. It can cause localised overheating though, which can then break your head gasket seal, which can then pressurise your system. The only causes of cold pressure are the head gasket, and maybe the EGR system (on NAFTA vans) if you are lucky.