You mentioned that you are going the lowered route. Are you planning on running 20's or 22's with wider than stock tires? If so, some of those wheels can get heavy, and rolling mass can play a big part in fuel economy. The 3.73's will be better in the city with being able to use less gas pedal to get moving as well as on the highway to keep them rolling.
Stock 20inch wheels and they are aluminum, So no rolling mass issues I am not changing the ratio to anything wierd since this is a stock ratio that is the standard equiptment. My truck was optioned with the 3.73 ratio. I didnt want it with that ratio but it was the only truck with the other options I wanted.
To use an example: My 06 2wd(see sig) had 3.73's stock with stock wheels/tires. When I lifted it, I went to 4.56's with 35" tires due to increase in both size AND weight. If only size was the issue, 4.30's would've been closer to the stock ratio. But now my new wheels/tires weigh ~40 lbs more each.
No offense but blah blah blah
My whole point is that you probably won't see as big of a mileage increase as you might expect. I don't think that you will find anyone willing to trade anyways, being that it's more than a basic swap. The PCM(computer) will also need to be re-tuned for the new gear size, or you will get ABS and brake system lights on the dash. Whatever you do, do not pay for a gear swap, as it will take forever to break even on savings. If anything, just slow down to 70
My cousin has the same truck but with the 3.23 and he gets 20-22 mpg on the highway, I get 16-18 so I will see a difference. I drive mostly highway and very little city. The speed limit where I drive is 75mph so slowing down to 70 might not be a great option for ME! I know about the pcm and I can have that taken care of.
If you really want fuel economy, should've bought a Prius. JFWY