I'm not sure there's a big mileage difference between the 3.73s and the 4.30s - while the 4.30s definitely increase the RPMs, I don't think that they use much more fuel.

On my truck - 2004 4x4 crewcab auto w/4.30 gears - I've gotten an all-time best of 13.5mpg and an all-time worst of 9.9mpg, and overall I'm averaging about 11.5mpg. Since all 8,000 miles on my truck were put on in the last two months, those are winter mileage figures - so summer mileage figures would probably be a little better. Also, at least half of those miles are with the hubs locked, and probably 1,500 of those miles I had the truck in 4-hi - and even running 4-hi I've only ever had two tanks that dropped below 10mpg (both at 9.9). While I've towed with the truck a few times, it's usually for less than 50 miles - so I don't really have any separate towing mileage numbers.

This is a mixture of perhaps 75% highway driving (at 70-80mph) and about 25% city driving. At 80mph I'm turning about 2,700-2,800 rpm - and my tires are 235/85r16s, which are about 32" tall.

Anyway, as far as I can tell the 4.30 gears don't seem to hurt mileage very much.

LK