check the battery for condition first that may be gining you all the codes. then check you rfuel pressure also the code 420 means is a catalytic converter but it cold be an O2 sensor not working as well.

battery voltage 14.7v while running, Has always cranked good.
Fuel pressure is 52psi at idle and will go up to 58 at a quick WOT
The o2 sensor paremators seemed a little low at .050v to.750v

when i said check battery for condition it doesn'tmean what it h as at idle. it needs to be load tested while not running after about a minute from shutdown. check for a vacuum leak if this is a 3.4 it may be a bad intake gasket leaking. also find offending cylinder that is misfiring an dmake sure it's not a plug or wire and check compresssion. check fuel pressure with key on and engine off if below 52 psi it's probably a bad pump it shold hlod pressure for about 10 minutes if not take to apro and let him check it out it may be an injector problem.

Had a crack in the intake manifold and could hear hissing, it so I replaced it. Seem much more responsive, but then after 5min I went back to being unresponsive I suspect faulty o2 sensors making the engine run too lean in closed loop.

Battery load tested came out as good.
Fuel pressure 52psi at KOEO and stayed there for 10 min
Good compression, plug wires, Ignition
Intake manifold crack repaired, no other vacuum leaks.
"MIL is off"

i suspect the scanner you are using is one form an auto store which won't read what the O2 sensors are actually doing. if they are working allright thenther eis no need to replace them but you need apro type scanner to find out if they are bad or not. because you have a code 420 or had that,check vacuum at idle if 15" or below suspect clogged converter on rh bank. as i think 420 is bank 2 . If you have a no mil light now andhave canceled evrything then also check for a clogged egr valve which can cause this . If the engine was running lean then it would activate the mil light. Other than that i have no idea what to tell you.

I actually do have a scanner that will view o2 activity. LT fuel trim % -14,

ST fuel trim around zero but it will fluctuate with throttle movement.

Can you get me a better diagram of the starting system. I think is one of those integrated PCM systems. Thanks

actually you never asked for a starting diagram but here it is anyhow... also a comon problem for starting is an ignition switch especially if intermittent.