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