My 97 Tahoe 4 door 4x4 with 3.42's got 19MPG HWY, we got 16 MPG pulling a trailer with a 93 Dodge Caravan home from Virginia.
I have had many MANY GM trucks, and aside from a 03 5.3L/4L80E/4.11 Yukon XL, I have never had an issue getting excellent mileage out of them. I average 16MPG out of the 03 with mods.
First, if you want mileage out of a truck, SCREW the cruise control, isn't going to happen. It constantly accelerates and push's the engine far to hard.
Learn how to drive a vehicle.
You have to learn the art of letting the vehicle drive itself.
Don't strain it at all, take your time and SCREW other motorists, if they want to get in a hurry, they can pay for your fuel.
Just because you are moving, doesn't mean you have to accelerate. Take your foot off the gas and let the vehicle coast as much as possible. It blows my mind when I ride with someone and they either brake or accelerate constantly.
If you are going down hill then up another hill, accelerate maybe the last 1/4 of the down and it will carry you up a good portion of the incline.
Keep the vehicle in high gear as much as possible.
Find your particular vehicles sweet spot, not all vehicles like to be driven the same.
If you were local, I could ride with you. I promise you, if you listen to half of what I tell you, your mileage will leap drastically. If we all leave at once, 9 times out of 10, I will be the first person there, so it isn't about driving slow.
My current ride is a 94 suburban 4x4 with 3.42s. I have an edelbrock performer TBI intake, ultimate TBI mod's, shortie headers, magnaflow Y-pipe with convertor, 3 inch dynomax exhaust. I am averaging 23MPG on my daily commuting, and I know there is more in there as I go.
As soon as I got my license at 16, I put nearly 25K a year on my vehicles. At one point, I was exceeding 85K a year on my vehicles. It quickly became obvious to me that I had to figure out how to get better mileage. I did as much research as I could, then monitored every tank of fuel. I practiced every technique I could until I got it right.
My personal best from a full size truck is out of a 87 GMC Suburban with a 6.2L diesel, 700r4/3.42s/30 inch tires. I got 32 MPG out of it constantly.
I am not some super mileage machine. I am well practiced and disciplined.
I taught my wife drive. If she tries, she can get better mileage then me. Her normal driving is usually within 2 MPG of my best in the same vehicle with only 1 vehicle exception. Our 98 Grand Cherokee 5.9 Limited, I could get 16.5 MPG if I tried. She could never get better then 13MPG from it. I had converted it from all wheel drive to a regular part time transfer case. You couldn't really blame her; the thing was such silly fun to drive it was hard to be an adult behind the wheel. Even my 63 year old Dad drove it like a teenager. 35-40 foot burnouts were the norm without using the brakes.
