So if there is no benefit to the 4.10 over the 3.73, tell me why a 3.73 is better than a 3.39? Why would a 3.39 be better than a 3.08? Why not just get a 1.0? The same logic applies at all of these comparisons. Where does a higher gear ratio make sense and why, and what are your qualifications or research to make that distinction? Your experience doesn’t count because that is YOUR experience and others’ will be different depending on how they use their truck.
Thousands of heavy duty truck buyers pick the 4.10. Are they all making a mistake? If you are buying an HD truck for use mostly as a daily driver, with occasional heavy towing, or use in mostly flat country, get a 3.73. If you are buying it to tow a heavy trailer in mountainous terrain, you will be happier with a 4.10. With a 3.73, you will spend a lot more time in 5th gear, or 4th gear, and be RPM restricted on speed going up long grades. Your truck will do a lot more shifting.
This ”first gear” only thing doesn’t make sense. A 4.10 provides 10% more power (and yes, 10% higher RPM) in any gear. It gives a different RPM, gear position, and power result across the entire performance range. This will be beneficial to some but not to others, based on the use profile.
The fuel economy issue is also not cut and dried. It takes a certain amount of energy to move a given load over a given distance. Running your engine at the peak efficiency point, for a given use profile, will provide the best fuel economy. The engineers at truck companies aren’t idiots. They offer higher ratio differentials for a reason - they are a better choice for some users. They have picked these ratios as the best compromises for they way customers use their trucks. They are not random choices.
The thing about extreme contrasts to disprove a point, is that it doesn't work when the point doesn't have extreme contrasts. We're talking 3.73 vs 4.10, and that difference is insignificant. I didn't say they'll pull equally hard off the line, because the 4.10 will pull harder from a dead stop.
But at 50 mph, the gear in your axle is completely irrelevant. You can get more torque two ways, bumping up your rear axle ratio or just downshifting a gear in your transmission. That's literally its job.
To get the final gear ratio, you multiply your transmission gear by the rear axle ratio. Doesn't matter if you increase the rear axle to increase your final gear ratio, OR, downshift the transmission to increase your final gear ratio.
Yes the rear axle provides more torque across each transmission gear, but you're missing the flipside of that coin which is, you're no longer necessarily using the same transmission gear at the same time in both trucks. If the 3.73 downshifts, it will likely be providing more torque than the 4.10 at the previous gear (haven't done the math on this specific case, but we've argued this on the 1500 forums extensively with the 3.21 vs 3.92)
The only place the transmission can't help you out is when both trucks are in first. At that point, the higher axle ratio always wins.
But there is no rule that says both trucks have to be in the same transmission gear at the same time. In fact, a lot of times they'll be in different gears (the 3.73 will likely be in a lower transmission gear vs the 4.10 a lot of the time.)
You can't bump up the rear axle ratio without also affecting what gear the transmission uses. It's that simple. In first gear, the 4.10 hits redline quicker so it needs to upshift before the 3.73 does, and then loses torque vs the 3.37 still cruising in first.
