WHAT YOU CAN DO WITH THE 4T60E
I decided I'd write this just because I know a lot of people with a 4T60E don't even mess with anything but overdrive since it's an automatic. I didn't for about a year, then I tried messing with L and D and seeing where it shifted and how you could tinker with it. So here is everything I know about driving the 4T60E. Be careful when doing any of the stuff described below, and don't blame me if something breaks because I'm just telling you how I drive my car. Not like this is hear for you to read and then go do with your car, ya know.
What does L do: You are stopped at a light. You put the car in L. You go. as you are going the car will not shift into 2nd gear it seems. That is until about 35-38 mph. L will hold you in first gear no matter how much gas you are giving it up until about 38 mph when it shifts into second. Once in second gear and in L the car will never shift out of second to third, you'll just bounce off the rev limiter at 86mph in second if you are in L. If you hit second gear, still in L, and are slowing down to stop, SHIFT INTO D or OD. If you dont, its not that bad, but the car will downshift prematurely into first and jerk kinda hard.
What does D do: D is basically OD but it will not use fourth gear. D is generally used for stop and go city driving.
Downshifting to first gear: Say you are doing 25 mph in OD or D. You want to be in first gear and be able to just go when you floor it and not wait for it to shift. If you just drop it in L the car with jerk as though you just kicked it in the nuts. So how do you get into first smoothly? There isn't any really good way, but there is a better way than just dropping it in L. What you can do is hammer down the gas to make the car downshift on its own and just as it down shifts put it in L and you can ease up on the gas and keep it in L. This must be done somewhat quickly or you'll be going too fast for it to still be in first gear in L. With the tachometer reading about 3500 RPMs at about 25mph you know that you are now in first gear. When you floor it from 25 mph in L in first gear, pop it up into D so that you can shift into second at a higher speed (read more about that below).
How to get the best runs: You're stopped at the track about to launch, should you be in L or D and should you be holding the gas down with the brake at the same time? Do NOT hold the gas down with the brake, reason being, I tested this at the track at many different RPMs by adjusting the idle possition. I test proved the fact that you get the absolute best times by simply having one foot on the brake and the other foot hovering above the gas waiting to mash it down when the light turns green. I tested this all the way up to about 1600 rpms from the average 700 rpm idle. You will also want to be in D when launching. The reason for this is that if you are in L and floor it, the car will shift into second at about 38mph (before 40mph somewhere) on average. However, in D the car will shift into second at about 41mph (past 40mph somwhere). Then, once the car shifts into second, you'll want to drop it down into without letting off the gas at all. You can shift into L at any point when the car is still in second gear (41mph - 70mph on average at full throttle). The reason for this is to manually be able to shift out of second gear into third. The car will shift for somewhere between 70 - 80mph in D. In L you can hold it till you bounce off the limiter ( which is a bad thing) at 86 mph.