Since you have an '04 like me, check the inside of the glove compartment door - there may be a sticker there that tells you which one you have. It's most likely a 3.55 or 3.92. Also, if it hasn't been worn away, mine has a tag hanging from the rear axle near that right spring mount or wheel that says "3.55 open", meaning that it's a 3.55:1 axle ratio with an open (non-limited slip) differrential.

 

Maybe also try resetting the PCM.Mine was a little sluggish once and i did this and it seemed to help a little after it relearned my driving habits.

 

how do i reset the PCM? and yes i have a 3.55 gear ratio

 

Actually, I make it a point to reset the PCM after cleaning the throttle body...

FAQ section has the DIYs for both...