As was said 3:73 gears with the low automatic ratios will give you lots of wheelspin in first gear especially. If you have stock tires, just be ready for that. 3:73 gears will give you better acceleration over all though. And shouldn't hurt around town gas mileage.They will only affect fuel consumption at highway speeds when you are remaining in one gear.
As for installation, any mechanic worth his salt can install them successfully. It all depends on competency, and patience. Gears installed correctly should never whine.
My 3:73 gears from the factory have a slight whine because Im sure that they just didn't spend the time to set them up right.
If gears are installed correctly with consideration given to keeping backlash within acceptable limits, they should be quiet. Backlash is simply the space between the mating gears. They cannot be fit too closely together, nor too far apart. There has to be a certain amount of "play" or clearance between the gear teeth. They would seize up and wear or break, otherwise.
6 hours of labor for install isn't out of the question. it all depends on how close the mechanic wants to get the tolerances and how fussy he is.
Installing everything clean, and burr free, with attention to detail is the key.
If / when you do decide to get gears installed, make sure you go to someone you know, or has a good reputation. And its worth it to replace everything, bearings, gears etc when doing it.
Ive done a few gear changes myself over the years and it isn't difficult, but as
Ive said, it does require a fussy approach. It isn't hit and miss. If done right, gears don't make any noise.Ever.
Im a machinist by the way, with 40 plus years of experience.
Just remember , you will have to get your ECU recalibrated to get the speedometer to work correctly.
2011 GT. Grabber Blue. Procharged. 3:73 manual.Billit LCA's. Corsa Extremes. GT 500 wheels. Racemaster DR's. T-56 Tremec. Dynotech DS . Centerforce DF. American Racing headers/high flow cats 560 rwhp.Donny Walsh tuned
2012 Pony Package. Race Red.3:31 automatic.BBK longtubes and catted X.FRPP Sport axlebacks. BBK throttle body. Dynotech DS. Brembo wheels and tires. Strut tower brace. Airraid CAI. Bama tuned.