6 speed manual transmission for a 1997 grand prix gtp?

I want to get a 6 speed manual to get better gas mileage and still get the same performance when i want it. is there a transmission that could give me the same performance as my hd transmission i have in it? if so would it give me any better fuel mileage. or if i could put an automatic 6 speed in there it wouldn't matter to me just want better performance.