2000 V6 Straight pipe

Why did you do this? Besides being illegal the car isn't designed to work with this set up. I'm not familiar with your car's O2 sensors but if they are heated and disconnected as Noobz347 said, you're going to have problems before even getting to their function and those problems.

For a lot of reasons I don't like what you've done and as Noobz347 pointed out with what you've done, you've done nothing to enhance your cars performance on or off the street. That said what is probably going on has to do with the cold start strategy of your PCM's calibration. I'm referring to the calibration that is on your passenger side valve cover and not the calibration on your PCM. During a cold start most of your emission sensors aren't monitoring emissions, they are monitoring the state of the sensors or sitting idle until the PCM turns the monitoring on because their operation is initiated by the state of other sensors which the PCM is also monitoring. Because of this, the calibration has a cold start strategy program to run the engine until all the requirements to monitor emissions are met. This cold start strategy isn't a learning or adaptable strategy. What's probably going on is you have created a condition that is outside the parameters of the cold start strategy and there are no fall back options from the cold start strategy. The cold start strategy is extremely liberal in its parameters but it's based on "as built" emission system and it won't recognize anything outside of those parameters which is why the car won't stay running. Because this is all happening before the emission monitoring system is up and fully running probably explains why you are not pulling any codes and if the "check engine light" should be on for this or not, I don't know so I can't tell you. To get the car to run you will need to program a new cold start strategy in to the PCM. Bear in mind that's not a "tune." This is actual programming and not altering parameters of the programed operating ranges already available. I also can't tell you if you will require a new running strategy\calibration for the engine or if a new "tune" alone will keep the car running when the PCM defaults to it's post cold start operating parameters. A lot of the engines features operate off of the monitoring of the emission system so I doubt any solution to running the car the way you want to is going to be accomplished with "little effort" or inexpensively. IMO your best option is to run the car as intended and I hope this convinces you to do just that.