You can't tell me that dropping RPMs ~13% on the exact same truck won't make me get better mileage. You of all people should know that one truck doesn't get the same mileage as a similar truck that comes right off the assembly line after it....
All the trucks that get good mileage on TDS.com have 3.55s. VERY FEW people with 4.10s get above 15, but most people with 3.55s get 17+.