I purchased a 2004 Gt it now has 73000 miles on it. When taking off in first if you steadily give it gas it is ok if you stick it, it will stumble for few seconds then begin to pull ok is better in 2nd but still nowhere near it's potential. Has new fuel filter. When I bought the car had a programmer in it for a 99-2003 not an 04 but had a tune in it I reset to stock and still is the same. Has 75 mm throttle body and no cats any ideas?