[Daytona]

The difference between 3 and D is significant. If you did not notice anything then you were not consistent in your launches or something else negated the difference because it is proven on all types of vehicles that there is a noticeable difference between the 2. For some vehicles it's more significant than others but there is a difference.

As for shifting vs. not shifting, auto transmissions are most commonly set up from the factory to run just shy of peak (if set up correctly) in order to minimize the chance of overstressing the trans and related components. We've all known stock vehicles that are purposely detuned by the factory to protect parts or get that insurance premium exemption. Is it better to leave it in 3rd vs. shifting? Only in the fact that you'll be a lot more consistent in your ETs by letting the car shift. Some trans have adjustable governors to allow you to fine-tune the shift points.

And if you put in a shift kit in the trans your car will be even quicker and just as consistent. Plus shift kits have the added bonus of shifting into the next gear quicker and with less stress on the trans as it doesnt stay at the top of a gear as long.

And I forgot to ask before but are your rims stock or aftermarket? Aftermarket rims, if meant for looks and not performance, are usually heavier than stock and that added spinning weight will slow down the car. It's not the weight similar to weight of something in your trunk but SPINNING WEIGHT. Sure there's the absolute weight difference (14 lbs. vs. 8 lbs., for instance) which matters, but spinning weight magnifies the effect of the added weight.