Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
There has been a service bulletin on the reaction sun gear, (updated part #) That is internal with the trans. Of course, you will want to check the fluid level. Here is what the bulletin states.
Bulletin No.: 00-07-30-022D
Date: June 10, 2008
Some customers may comment on a no reverse, no second or no fourth gear condition. First and third gears will operate properly.
The reaction sun gear (673) may not hold inside the reaction sun shell (670).