Alot of people have either or on the gears you mentioned as a DD. I always say..don't fear the gear. Your city usually will go up 1-2mpg and hwy could go down 1-2 mpg.
__________________
1995 Mustang GT-Heavily Modded-Sold 2003 Ford Lightning-Sold 1997 Saleen-5.4 conversion-Sold 2005 Mustang GT-Torch Red-Sold 2003 Mustang Cobra-Oxford White 2003 4Runner V8 Sport Edition 4X4
I noticed better mpg after getting 4.10s in my GT. (20miles more on a tank or so) But its thirsty on the freeway and a real long trip probably wouldnt be too fun
__________________
-2000 Mustang GT Ford Racing 4.10s // T45R 5speed// Hawk HPS Brake Pads // Cold Air // BBK 75mm TB // BBK X-pipe // Hooker Aero Chambers // Eibach Sportline's // Ford Racing Upper and Maximum Motorsports Lower Control Arms // '95 Cobra R's // Toyo Proxes T1-S // Steeda Tri- Ax Ram HDX Clutch // tuned w/ SCT X3
i've aways heard 3.73's for a 5 speed, 4.10's for a manual. buuuut, i have 4.10's on my auto, and i love em. driving a long way on the highway does sck though, its about at 2700-2800 rpm at 70 MPH!!!!
__________________
2007 Satin silver 4.0-"Sadie"- Dual Pypes Violators, JLT CAI and 93 bama race tune, motive 4.10 gears and FRPP T Lok BEST E.T.- 14.485 AT 94.1
1985 Regatta Blue 'vert 5.0 LX-"Sally" 87 5.0 motor, Holley 600 4bbl carb, edelbrock high rise intake, MSD ignition, 1.7 Roller Rockers, underdrive pulleys, A/C and smog delete,BBK O/R H-pipe, flowmaster American thunders. transformed from a 3.8 to a 5.0!
i've aways heard 3.73's for a 5 speed, 4.10's for a manual. buuuut, i have 4.10's on my auto, and i love em. driving a long way on the highway does sck though, its about at 2700-2800 rpm at 70 MPH!!!!
i know that.......i didnt say i had a manual. i guess to be more clear i should have said "i do have them in my auto, but my friend had 3.73's in his manual, and has since upgraded to 4.10's after driving mine"
__________________
2007 Satin silver 4.0-"Sadie"- Dual Pypes Violators, JLT CAI and 93 bama race tune, motive 4.10 gears and FRPP T Lok BEST E.T.- 14.485 AT 94.1
1985 Regatta Blue 'vert 5.0 LX-"Sally" 87 5.0 motor, Holley 600 4bbl carb, edelbrock high rise intake, MSD ignition, 1.7 Roller Rockers, underdrive pulleys, A/C and smog delete,BBK O/R H-pipe, flowmaster American thunders. transformed from a 3.8 to a 5.0!
my city mpg went up just a little, highway mpg stayed about the same for me, but only because i used to go ~80mph, and now i go about 55-60mph; just to keep my rpms below 2,500.
it's nice, because at 45mph you can cruise in 5th gear. ( i could drive even slower in 5th, but the aluminum flywheel is a little harsh at low rpms).
bottom line, the car accelerates easier and is more fun to drive. i definitely suggest this mod.
gears question? 
/
