You will not hear this from any GM dealer or tech.  I hope this information saves someone from the BS I have been thru.
The durmax computer has a learning mode and uses stored data for engine, injector control!  Read below:

Well I fixed the problem with my 2003 duramax last night by disconnecting both batteries and forcing the computer to do a cold start. Imagine that.
When I picked up my truck from the dearler after the injector change, I noted that the clock had the right time and the radio stations were still set correctly.  I challenged them on the fact that they had done the injector change without disconnecting the batteries and they said they had.  I also asked them if the computer had a learning mode and they told me NO.
After I did the cold start on the computer I drove 10 miles west and watched the MPG hover around 22 MPG @ 65 MPH on the tirp out and back.
I then went and hooked up my  5th wheel (35' Titanium) and pulled it 57 miles averaging 9.7 MPG.  We had a 30 MPH wind out of the north and the 30 of those miles were into the wind.
I turned around and come back south with the wind and got 12.9 MPG for the next 30 miles.  Just like it used to do before the dealer changed the injectors.
I guess I am not surprised by the ignorance of the GM dealers and technicians on this engine.  

That's a good tip. Thanks for the heads-up.