Switchin to that tall of a gear makes no sense unless te truck stays on the highway at ALL times. And that flat highway, no hills. He'd have no power, meanin he'd be in an out of OD, meanin he'd burn up the tranny quicker than he'd get money back from savin on gas. It is a truck, won't get 20+ without straight highway drivin anyways.

Free tips, don't gun it at every stop light, keep tire pressures up, and don't go over 70 on the highway

 

Country 09, I do not agree at all with your statement about the tranny hunting gears and not having power.
I have owned a tall geared Chevy, with the six cylinder and a three on the column.
With that old school set up and 3.07 gears it was no rocket ship in stoplight wars but it was still useable and on the highway it was amazing at mpg.
You can get the Silverado with 3.42 and 3.08 gears from the factory.
You get used to the slower accceleration at lower RPMs but the request was for MPG increase. in traffic the difference is not noticed. The lower RPM at cruise will give you the MPG
The cost of a gear swap is also very expensive unless you salvage gears from the local junk yard.
Country 09s last statement is the best advice for you if you keep the 4WD V8 truck.
There is no miracle fix for MPG with a 45000lb vehicle.

 

Damn ,I meant a 4,500lb vehicle.
I get used to lbs X 1000 on my work vehicle. It weighs 695,000lbs and is very fast.

 

Generally a factory Chevy that comes with a 3:42 and a 3:08 are the new ones, with a 6 speed transmission and they don't suffer near as much gettin up with the added gears. The did put 3:42s in z71s around 04-05 to reach mpg goals, yes. But those things are turds and lack in every aspect of havin a truck. With 3:73s and 33x12.5x20 toyo mt's I get 15 mpg mixed highway/city and I consider that great for a z71 extended cab truck. If he's wantin the kinda gas mileage that warrants goin down to a 3:08 or taller gear, then he shouldn't drive a truck honestly. Use a truck as a truck, they're not meant to get great gas mileage, and with tall gears like that, yes he'd be in and out of OD like nobodies business. I do it not with the gears I have and 33s. The 3-4 band in these trucks is the weak link and will burn it with him goin in and out like that in a matter of months

 

so headers increase mpg on vortecs? i thought they made it worse?

 

Better airflow=better mpg. But with the added power you'll likely not see the increase because you'll stomp it everywhere. I think the bigger increase in mpg is on highway

 

on my 07 4.8 I put a cold air tube/a house aluminum dryer hose in place of my plastic air box between the filter and tbi ,and alaigned the front end to zero toe in and gained a 1 1/2 mpg.
Merry xmass

 

Keep things stock and clean the mass air sensor with electrical contact cleaner(rubbing alcohol and cotton swabs).

 

Smaller, lighter and narrower wheels and tires, but then that sort of defeats why people buy the truck. Bad mileage is part of the deal! Been there myself but then I started doing numbers on the cost of gas for a year and how much I would save and didn't seem worth it.