A4 Q's
 

Does all 98-02 camaro/firebird come with 2 D option? [D] and D. Which is good for daily driving both street and freeway? I usually just drive with the D just above the 2&1 and the car seems to be louder and the car really slows down when I take my foot off the gas pedal, mostly on the freeway. Is that normal..?

On the Chevy it's 1-2-D-OD

On the Pontiac it's 1-2-3-D

The reason you are experiencing that is because you are in 3rd gear and not 4th (overdrive). You are running a higher RPM. Use overdrive for the highway and freeway.

The reason it slows down more in D than in OD is because in D the over run clutches are in use, they provide engine braking.

Will it hurt my transmission when I use D instead of [D] on the freeway...? Which one is better for Gas mileage??

That doesn't make any sense because the 1/2 support roller clutch is overrunning in 3rd AND 4th gear. Are you talking about a 4L60E? Maybe you are familar with a different type of transmission.

I thought it was more of a gear ratio thing slowing the car down.

Yes I'm talking about a 4L60E, when you shift it to third the over run clutch comes on and it provides engine braking.

It's probably a combination of the two.