What kind of driving do you plan on doing?? Does the truck you are looking at have a 6liter or a 8.1? I would recommend finding a duramax because you will see about 30-40% better fuel economy, more on demand power, a turbo , and cheaper fuel prices. My mom gets 22mpg out of her completely stock 2006 2500HD Duramax crew cab

 

Yeah, I've "spent the ranch", but I spread it out over a period of years.

I spent 1400$ on an aerodynamic fiberglass cap. With 3MPG gas improvement, it took a couple years to pay for itself, but I was using it for camping, anyway.

The other thing which gave my mileage a major boost (3MPG)was reducing from 410 to 342 differential gears. I replaced the bearings at the same time, so it cost 2000. I waited till I was going on two major trips, so that helped pay for itself in improved gas mileage.

Of the two, the more dramatic gas savings was the 342s, because it cut my city driving gas bill in half.

Any way you deal with tailgate wind resistance, from removing it completely, to using a tonneau cover or a cap is going to save you a lot on gas.

You may need(or want) those 410 Differential gears, for power, especially if you don't spend a lot of time on the highway.

 

The cheapest way to save on gas is to remove your tailgate and install a tailgate net; they're approximately $30.

 

I dont believe no tailgate will save you gas in the city during stop & go situations, thats where I loose my MPG. I cant imagine spending hundreds even thousands of dollars at once to save a few MPG. I am fine with my highway mileage but can see that a tailgate will cause friction and removing it might save a few dollars a month, its the dam city that gets me, but I chose my truck for a reason.

 

I guess it depends on how many highway miles you do...

 

i had 3.42 gears on my previous 06 z71 (5.3 motor) and it sucked so bad. i have 4.10 with my vortec max 6.0 and love them, i cant imagine spending money to switch from an awsome gear to a lame gear.(4.10 to 3,42) especially in an hd truck. if you want good gas mileage get a prius. trucks are made for towing and hauling not 35mpg's.

i got 14-14.5 with my 5.3 now i get 12mpg with my 6.0 (both half tons) and i couldnt be happier. because the 6.0 has power when i need it.

i get 35 mpg city in my pos saturn that i paid $400 for. so i drive that to work and drive the truck everywhere else.
the Hd trucks do have a better transmission and rearend. but if you are looking for a nice in between look for a vortec max 1/2ton. a little better trans and the 14sf rear end.