Man can I tell you what a difference! These gears turned my car into a beast! This is the first thing you should do for your mustang and you won't regret it. All I need now is some bigger rims/tires! haha
Had Bill and his staff install these gears after I had the SCT 93 tune and JLT CAI. The change from the original 331's was unreal. The car responds so much quicker and the loss in gas milage was negligible.
FRPP 4.10 gears work well with Mustangs. Nowadays all Mustangs come with an overdrive gear or gears in the transmission which keeps the highway revs down with 4.10 gears. There is no need to be concerned with mpg loss or high revs on the highway like in the old days. These are the gears Mustangs should come with from the factory. FRPP gears set up easy and are known for being dead quiet with a proper installation.
I wanted a little more jump off the line, and more "go" through the gears, and this 4.10 upgrade did the trick. My 06 GT feels more alive. Yes you do see a few more RPM's at cruising speed, but I didn't really notice a difference in fuel economy. Not a job for an inexperienced mechanic, but a relatively cheap & easy job for a good shop. While you've got the "pumpkin" open you should replace bearings, gaskets, etc as well. I rebuilt my LSD with a carbon fiber disk kit while everything was apart, and I topped it off with a new girdle for some more strength (and it looks great too!) Don't fear the gear, and you'll be thrilled with the results.