ok, when you manualy shift an auto it will stay in the gear you put it in, 1st it stays there until you shift it to 2, by running an auto in3(3rd gear on 4th gens) D(3rd on 3rd gens) you are not allowing it to go to overdrive(4th) I launch in 2, the tranny still starts in 1 and I allow it to shift itself to 2, then I wait until i want to go to 3(3rd) gear when the revs are high enough, sometimes i will leave it there sometimes I shift to D(overdrive) My car reads 1,2,3,D. Some people think that you should leave it in D (overdrive) and let the tranny shift itself well this doesn't allow you to make peak HP in any gear as the tranny will shift at slightly lower than max RPM. By shifting it manualy you can leave it in the lower gear until max RPM is reached and then you select the next gear. Now there are a couple of tough things here. 1) you don't want to over rev your engine so you have to know how your car shifts so you select the next gear and leave time for the shift because the revs are still climbing and can overshoot a safe RPM limit. Next you need to know your car's limit if modified. if you are making the shift at 5,700 and with your mods the max HP isn't achieved until 6,000 you are not taking dfull advantage of your HP. I start in 2 and let the computer do the work because 1 is a real short gear the way my car is geared (it only lasts a few seconds)
Doug