I am having trouble with cold starts. The truck cranks fine, starts and idles great for a few seconds, then shuts off. When I try to start it again it is very difficult to keep running (have to pat the gas pedal), it backfires and it smells like gas is pouring out of the tailpipe, but it's not.
We have replaced the TPS, IAC, ECM and all the tune items. After it has warmed completely it runs fine.
HELP

 

Possible your CTS, (aka ECT engine coolant temperature) as this sensor feeds you PCM with info.
The coolant sensor is extremely important because the sensor's input to the PCM affects the operating strategy of the entire engine management system. That's why the coolant sensor is often called the "master" sensor. It will affect the start up fuel enrichment on fuel injected engines.

Keep in mind this is just what I've read, and have not experienced this problem...but I think it's worth a shot since you changed out a bunch of other sensors.