rear end/gear question about the E350, 7.3L

[fswaney]

I need to put a new axle on my E350, 7.3L former ambulance (it is now an ice cream truck, and all the ambulance stuff is basically stripped out.)

are the rear axles interchangeable? also do y'all foresee any problems with going with a 3.54 or 3.73 gear ratio? the freezer that I have in it is an ultralight modern ice cream freezer that I run off a power inverter. fully loaded, we're talking maybe 400-500lbs. do I really need the 4.10 gears? I'd like to get a gas mileage gain that the lower gear ratio would provide. I appreciate your thoughts/feedback.

[Gasser Hater]

I have a 2003 e-350 that currently gets about 11 mpg with 4:10s. I just ordered a tuner from dp and I'm definately swapping out gears to 3:55 first chance I get. I'm sure you would have no problem doing the same. From what I read all the time, With the right kind of driving and the right setup its quite possible to see 22 mpg with these vans. I'm not swapping axles, just the gears. I'm also installing a locker while I'm in there.