Gears & Axles - 3.90 help!

I need some advice on 3.90 gears. My car is stock and has a manual trans. I've heard that with 3.90's I will need a new diff? Is this true and how do 3.90's perform?

as far as I know,and I could be wrong ! 3.90s' are only available for a 3 series carrier which you would have with a manual trans. auto trans with the 2.73s' would need a different carrier.

auto w/ 2.73 = 2 sereis
auto w/ 3.23 = 3 series
manual w/ 3.42 = 3 series

I just did 3.90's on my 2000 z28 you dont have to get a new diff but i would deff get a girdled cover. As far as how they preform i love em car pull hard in every gear 3rd, 4th are awesome, and it makes 6th useable. They are dead quiet also.

I just did 3.90's on my 2000 z28 you dont have to get a new diff but i would deff get a girdled cover. As far as how they preform i love em car pull hard in every gear 3rd, 4th are awesome, and it makes 6th useable. They are dead quiet also.

Sweet! So how much was the entire gear swap??

I just paid for parts cause i did work myself but after buying everything it was right about $500, best mod ive done so far.