I'll play too:

1998 sr5 3.4 SC'd 2.0 pulley, 7th injector 40k on motor. must run premium!
5-speed
Dual Transfercases
4.88:1
35x12.5R17 Goodyear MTR's
4inch lift
Rear Disk Brake conversion
Rear Full Float
no front or rear bumpers

Average milage 12mpg town or freeway.

I have a lot of extra drag with all the mods.

2000 3.4
5-speed
Bone stock
Fresh tuneup (plugs and wires) 1 month ago
265x70R16 c loads
255K
When I first got it and got it up and running I was getting consistently getting 14mpg around town. Not had it on a road trip yet.

Last week I seafoamed the upper intake and ran a can through the crank case for a tank and a can in the gas tank. Then new oil change.

Since then I have had 2 tanks of gas go through it have got 17mpg around town. I suspect that freeway I will be in the 20 mpg range, and I get to run low grade gas.

Year: 1996
Tire Size: 285/75R16
Gear Ratio if you know it: 4.30
2WD or 4WD: 4WD
Modifications that affect MPG: mud terrain tires, 3" lift
Automatic or manual transmission: Auto
4 cyl or 6 cyl: 3.4 V6
Current highway fuel economy: ~17

This is considering the road is pretty flat and there's not a lot of wind and when going about 70MPH. If I go 50MPH for a while, I can get up to 23MPG! I've noticed my rig prefers that speed for fuel economy as it's right around when the torque converter will lock up and the RPM is at it's sweet spot.

Awesome! Thanks everybody! Anybody else want to contribute?

1998 3.4L Auto

Getting 18.8 on the road right now from Monterrey, MX to Waco, TX then to Austin (~700 miles). Fully loaded with a 20 cubic foot Sears cargo box/brick on the roof. Keeping it at the speed limit (75) or a bit above with the flow of traffic. I use cruise control a lot. New Michelin Defender LT/X 265/75/16 and 4:10's. Very little altitude change.

How well does the truck cruise at 75 with that set up?

My info with some statistics from my phone app thingy that I started using toward the beginning of the year...I think.

Year:*1997 LTD
Milage: 430k+
Tire Size: 265/75/16
Gear Ratio: 4.30
2WD or 4WD: 4X4
Modifications that affect MPG: None
Current highway fuel economy: 21
Automatic or manual transmission: Auto
4 cyl or 6 cyl: 6

Year: 1997 Limited
Tire Size: 265/75R16 Load Range E, Mud-Terrain Tires
Gear Ratio if you know it: 4:30
2WD or 4WD: 4WD Push Button with RR Diff Lock
Modifications that affect MPG: 3" Lift
Current highway fuel economy: Approx. 15 MPG
Automatic or manual transmission: Automatic
4 cyl or 6 cyl: 5VZ-FE (V6)

Vehicle is in need of a major tune-up (Fuel Filter, Plugs, Wires, (maybe even coils), 2x O2 Sensors (non-cali)). And also needs new U-Joints.

Nice. What phone app is that?

for me a lot depends on time of year. Summer with 265/75/16 KO'2s highlander springs, few other minor mods, I can expect 20mpg
and of course if I'm playing in the back roads, less

winter, I think they put more ethanol in the fuel up here where our day temps are rarely above 36. studded 265/75/16 tires, more 4wd use and more locker use
16-18 maybe have not seen it go under 14 and that was last winter when I was constantly in 4wd and 105 inches of snow on the ground.

2000 v-6 auto, borla muffler, spectra intake. Plugs and wires have about 30k on them, running all synthetics

Year: 2002
Tire Size: 285/70R17 BFG K02
Gear Ratio if you know it: 4.88
2WD or 4WD: 4wd
Modifications that affect MPG: 2UZ , Mild lift
Current highway fuel economy: 18.2
Automatic or manual transmission: Auto
4 cyl or 6 cyl: 2UZ 4.7L V8

Fuelio

I just bombed down 101, currently sleeping in a rest stop somewhere north of San Luis obispo. With my scan gauge, going dead flat at 55-60 mph I think I'm averaging about 25. Overall for the whole trip it's about 22-23 over about 2000 km but that included some really rough windy roads in the lost coast s of eureka. 3.4 v6, manual transmission, no lift, Michelin ltx's balding, 265/70 r16, custom roof rack with wind faring and bike on the roof ( laying flat). I don't know why my mileage is so high but it's true. I've verified the odometer with the 5 mile highway calibration marks. It was 2 mpg higher on a previous trip without the roof rack.

2001
285/75R16E
4:10
4wd
3" lift
17.3mpg
Auto
3.4L

After a 1400 mile trip from Ohio to Colorado (first long trip with the 1999) this is what I'm seeing. I averaged about 74 MPH or so. A little faster than I usually drive but I was anxious to get to the mountains!

Year: 1999
Tire Size: 265/70R16
Gear Ratio if you know it: 4:10
2WD or 4WD: 4wd
Modifications that affect MPG: None
Current highway fuel economy: 18.3
Automatic or manual transmission: Manual
4 cyl or 6 cyl: 6 cyl

A couple things to note about driving in the winter:

Most people blame lower MPGs during the winter on the winter fuel blends, but there is another factor that plays in much more: air density. Winter fuel blends have been shown to yield about 2% less energy whereas an air column at 20 degrees Fahrenheit is about 10% more dense than an air column at 70 degrees Fahrenheit. That means the vehicle is working quite a bit more to maintain a given speed in order to overcome the denser air during the winter.

So, if I've seen a 10-12% reduction in fuel mileage due to the combination of winter blend and denser air, my equivalent summer average would be a little over 20 MPGs, all other things constant. I still need to do a tune up so hopefully that goes up a bit more.

Great for being 20 years old. No problem maintaining speed but you can tell a lack of power going through hill country in Texas, which really isn't a good test for altitude change. Overall very happy with the setup.