[RIP]

Welcome aboard. Need your model year and engine size in all your threads to give accurrate info. The codes you need to pay attention to are 54 (no camshaft sensor signal), 21 (O2 Sensor), and 31 (EVAP system failure). 12 just means the battery has been disconnected in the past and 55 means the code readback is complete. Your lack of a camshaft sensor signal is likely causing your stalling issue.

Camshaft sensors cost $20-30. Even at the dealer (depending on your model year). May be the sensor, may be a loose/corroded connection or bad wire harness. I would burn 3 minutes inspecting it before vacating your wallet. On the 3.3 and 3.8 ltr engine it's located next to the thermostat housing on the top passenger side of the engine. On the 3.0 ltr it's in the distributor.

A bad O2 sensor could effect stalling issues but, I would expect not to the degree you're seeing it. Can cause rough running/hesitation and less mpg or you may see no symptoms at all. I'll leap and say you have two O2 sensors, an upstream and a downstream. Your upstream (in front of the cat converter) sensor has the fault. It sits on top of the exhaust manifold on the back of the engine. Again, could also just be a harness or connection issue. Cheers!

You can drive forever with an EVAP system failure if the check engine light doesn't drive you nuts first.

First step would be to reset the codes ideally using a scanner. Short of that, disconnect the battery a couple minutes. Once done drive it around and make sure the same codes return. You don't need to waste time chasing false codes.