Do not mess about with fueling until:
1. You have a wideband O2
2. You know a lot more about tuning engines;
Point 2. can be corrected by buying Greg Banish's book Engine Management: Advanced Tuning
and reading it 2 or 3 times.
Also the stock tune runs pig rich at WOT to begin with, especially on the '02 to '04 GTs with the pink 21 lb/h injectors. I have seen some running 11.0:1 or richer at higher loads and WOT. Most tuners pull 0.5 to 1.0 "AFR" from the Stabilised Open Loop Fuel
table in the higher load and rpm cells...
- 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq