Gear swap info/help pls

[BP68]

Hey all. This question regards my 06 Silverado, but I figured the info may apply in general.

I have a 2006 1500 Silverado 2wd extended cab 5.3
I have 275/55R20 's and a stock 3.23 gear. (came with 17s stock)
Ecm has been programmed to correct speedo.

The truck runs very well, but I would like to wake it up a little.
I currently get an average of about 15 mpg with mostly stop and go city
traffic. Some times closer to low 14s when hot with air on. Sometimes in 16s when cooler and windows down/ no a/c. Plus I don't baby it, yet don't floor it red light to red light.

I am considering a 3.73 gear swap. Anyone done this? Speculated fuel change up/down.

I work at a dealership and have noticed that most Tahoes/Avalanches that have factory 20's seem to usually have 3.73's also.

Currently the truck seems to be slightly "bogging" when running between 45 -50 with converter locked up (approx 1200 rpm)

If I drop into 3rd and lock up kicks off rpms come up and the engine sounds happier.

Some people tell me the 3.73 will kill gas mileage
Others say the it may stay the same or slightly improve (due to current lugging)

Pls offer up your advice/opinions/experience.
I want a better driving/power feel without totally sacrificing daily economy since it is my driver.

Thanks

[mclairmo]

Personally, I would calculate what gearing you need to return the effective gear ratio back to stock specs and go with that. The factory probably has already scoped up the best overall combination for economy, power and reliability.

[69TowRig]

3.42s would be a middle-ground between the two. 3.23s are tall gears to push. It really depends on what you had for stock tires, do you remember the size? What you have now is ~32" tall.

As for fuel mileage, it somewhat depends on how and where you drive it. Flatland cruising might see a small drop since the engine is revving much faster, but on the flip side if it is lugging right now on the flats it might improve things. It will reduce the amount of transmission gear hunting since lower gearing will keep you higher in the power curve.

[BP68]

Originally Posted by 69TowRig

3.42s would be a middle-ground between the two. 3.23s are tall gears to push. It really depends on what you had for stock tires, do you remember the size? What you have now is ~32" tall.

As for fuel mileage, it somewhat depends on how and where you drive it. Flatland cruising might see a small drop since the engine is revving much faster, but on the flip side if it is lugging right now on the flats it might improve things. It will reduce the amount of transmission gear hunting since lower gearing will keep you higher in the power curve.

Stock tires were 245/70R17

It has the light duty power package with locking rear diff and HD trailering.