I just did a long road trip with my GT and got error codes P0171 and P0174 (These codes say I am too lean). I have never got error codes before and have been running my JLT CAI for several months with no problems. I cleared the codes and didn't get them again for the rest of the trip (150 miles and no codes). I am running 91 tune with 92 gas (I don't have 91 or 93 octane around here). I also notice that if I run in 5th gear for a while (manual transmission), then shift down to 4th and gun it, the car will hesitate for a second, don't know if it is a misfire or what.
I have read forums on running to lean or too rich. I am nervous about ruining my engine. Should I go back to 87 tune and 87 octane regular unleaded?

 

Perhaps you got a tank of cheap gas? I know when I travel from CA to AZ there are a few gas stations along the way that are questionable.

/me shrugs