I would first test if fuel pressure is dropping to low when engine sits for longer than say 5 hours
2006 runs 55psi fuel pressure, when off the fuel pressure should hold above 30psi for many MONTHS
When you turn on the key the fuel pump only runs for 2 seconds, its a safety thing, and then will not run again until RPMs are above 400, engine started
If fuel pressure is leaking out when truck sits then that 2 second run time might not be enough
So turn key on then off, repeat 3 times, 6 second run time, THEN try to start the engine and see if its better
If that doesn't help then I would change the ECT sensor on speculation, its not too expensive
ECT sensor tells the engine computer how much Choke to apply to a cold engine
Cold engine needs to be choked, computer does this based on temp it gets from ECT sensor
If ECT is showing a warmer temp than actual temp there is not enough choke applied for quick start up, but after a few seconds the cylinders are hot enough to not need full choke
There are two temp devices on the 3.0l engine
ECT sensor uses 5volts and will have light green and gray wires, only used by the computer
ECT Sender uses 12volts and will have red and black wires, its only used for dash board temp gauge
So they are not interchangeable
IAC Valve reads like it is working OK
It should be wide open for start up, so 2,000RPM surge
Then computer will start to close it for cold engine idle, 1,100-1,500rpm depending on outside temp(ECT sensor Temp)
Then as ECT/engine warm up the computer continues to close IAC Valve until warm engine idle is set, approx. 750-800 for automatic trans, lower for manual