Launch the car in 3, don't bother manually shifting. The computer can shift faster than you and it is hard on the bands when you do it manually. Why put it in 3? If you do happen to shift into 4th at a high speed it's not good for your tranny. A gtp with a modified pcm(DHP) will shift into third at WOT around 92-95 mph.
Turn the traction control off and turn on performance shift. Hold the brake and rev the car anywhere from 1300-2000 rpm's(each car is different) let go of the brake and slowly roll into the throttle. If you just give it full throttle you'll spin through first and you don't want that. You want a few chirps to no chirps. Some say count to 2 using one one thousand-2 one thousand and in that time you go from 0 throttle to WOT. Experiment with what your car likes and try to go as fast as possible without squeeling the tires. Also as you modify the car you have to learn the new mods as far as launching is concerned.
