We also have a Tahoe for towing duties and it's also my wife's daily driver (her commute is quite short).
I used to have a Silverado as my daily driver and I used it for towing. Then I started looking for a Tahoe so I could get a Civic for my longer commute. Since I was already familiar with these rigs, I knew what to look for and I specifically picked this year and drivetrain for efficiency.
Her Tahoe is a 2005 4.8L, 2WD, 3.42 gears and was already lowered by the previous owner. As a 2005, it has the low air dam and the electric fans. Stock, other than the wheels and lowering, my wife regularly gets 21-25mpg highway. She simply sets the cruise control and goes, A/C always on...
You could get an '05-'06 Tahoe air dam and hook it up to your bumper for the OEM look. Look into the e-fans as well. It's easy to mount the '05-'06 fans on the older Tahoes, but you need someone to reprogram the ECU to trigger the fans.
You get better mileage than we do while towing (11-12mpg), but our trailer is a brick and it's way too tall. The high gears in ours don't help either, since with the trailer O/D is basically unusable (I'll kick it into O/D down hills, but that's about it)
On my Silverado, I left a hole in one side of the grill block since the tranny cooler is on that side. I pulled the upper block off while towing.
Good luck!