It sounds as if you are running the TFI that keeps the 02 sensors in the system, the 1440st.
Here's the setup and adjustment instructions. If you enter the settings and go to page 3 here, look for the instructions in section 4B (
the yellow mode )for the accelerator pump feature, and lower that feature a bit. You will not really notice the difference in performance but it will make a difference in MPG.
If you're not sure about it, take it back to the dealer that tuned it and let them do it so you don't change the wrong setting. If it were the 4 pot system, I could tell you how to do it here but this system is more complicated to explain.
Electronic Jet Kit Instructions