I have an LS4 in my Fiero and have had HP tuner used to remove the Dif score tranny issue I had.
My question is with out a dyno to tune the car what would the most common changes be to the ECM to help performance?
The tranny is WAYYYY to soft, I want MUCH faster shifts, speed gov, rev-limmiter and so on?

Thanks.

 

you got the right idea. For an inexperienced user that would be the way to go. Other than that just tune the maf and watch out for KR. There is a lot to be gained by tweaking the tranny and TM.

The a/f ratio and timing aren't too bad on the gxp's. Way more aggressive than the LS1 tune at least.