If you are not pulling than you would probably be best with the 3:55. My
>'89 Bronco 5speed has a 3:55 limited slip axles and has performed great off
>road but sucks for pulling. My '00 F250SD PSD has 3:73 limited slip and
>pulls great, haven't been off road yet but don't anticipate any trouble.
>One thing to keep in mind from personal experience: if you plan on going
>off road and getting into anything slippery (mud, snow, water & rocks) get a
>limited slip axle. I know with the Super Duty trucks the only LS axle
>available is the 3:73 (according to forddirect.com). Not sure what the
>options are on the Expedition.
My '02 F350 V10 has 4.30 LS rear end. I can bomb down the freeway at
85 all day with no problems. (other than that slurping sound coming from the gas tank. hehe)I do tow a trailer full of toys to the desert on occasion and even with the 35" tires on it, I pull most hills @65/2000RPM and it chugs along at around 1700 RPM on the flats..
I've taken the beast off road in mud, hard packed dirt, shale and sand and the only time I've had an issue was in damp sand with 50lbs of air in the tires. Knocked the pressure down to 20lbs and it went everywhere I pointed it. The gearing is plenty for smokin' those meats pretty much on demand and the only downside I can think of is the higher engine RPMs on the freeway. I personally wouldn't change a thing.