Habbi - Thanks for clarifying. Things really get complicated when you try to compare the performance of one brand of truck to another, even doing identical tasks. I know I got better gas mileage pulling my trailer with my old, 6-cyl Nissan Frontier than I do with my F150, but I sure find pulling it a whole lot easier with the bigger vehicle. The combination of engine size, vehicle weight and gearing in the GMC may be making the difference.
If you have 3.55 gears, your truck doesn't have the factory tow package I think. So that, in combination with your tire size may make it hard for you to beat the GMC. Think of it this way: your truck might be "factory optimized" for "non-towing" driving. Yes, a programmer can help, but you may not be able to expect miracles.
Out of curiosity, what kind of highway mileage do you get when NOT towing? I currently get between 15.0-15.5 mpg. (This is on long Interstate trips.)
- Jack
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