Even a stock 03 with the stock 3:55's has enough low end torque to rip off 1.7 and lower 60' times all day long. Lower gearing is not the answer, traction is! Get yourself some good sticky tires and prep the hell out of your IRS and you can rip off 1.7's in your sleep. The stock 3:55's are just fine. Lower gearing will NOT lower your 60' times in this car with no other modifications to the rear suspension. On the other hand, modifying the IRS and leaving the 3:55's alone WILL net you lower 60' times. The IRS sucks when it comes to drag launches. If you really want to do a lot of drag racing in your car you may want to look into swapping the IRS for a straight axle out of a GT. That's what many of the serious drag racing 03/04 guys do.
U.M.