My two cents:
For one thing, 4.10s vs 3.73 doesn't mean throwing away 10% in fuel economy off the bat. IT DEPENDS, it's just math. How fast are you driving? What's the engine load? Which engine? Yes, there's a ~10% difference in gearing, but not all of that will show in your gas receipts because there's a lot more to it. In my own, specific, personal use where I'm driving 65+ mph when it's freeway time and have plenty of power at lower rpm, the 3.73s work better for me. In even mildly hilly terrain and/or 55 mph speeds, you may find that the 4.10s work much better and doesn't force the hunting in and out of overdrive all the time. Tires effect gearing too, so a 285/75-16 on a 4.10 is pretty close to a stock 265/70-16 on a 3.73. The point is, you can't make a blanket statement.
Also, there are differences between a 1500 and 2500 beyond the motor. The biggest difference to consider is that the 1/2 ton will have coil springs in the rear, where the 3/4 ton will have leaf springs. This means a lot to ride under load, sag, axle articulation off road, and how they deal with a trailer. Not that one is automatically better than another, but it's certainly different enough to consider. The front torsion bars on the 3/4 ton are considerably longer (rear mount is further back), and the bar itself is thicker. The 1/2 ton will have smaller brakes (both calipers and rotor thickness/mass), already a concern in this vintage Suburban. If it's a 8.1L it will have Hydroboost brakes and power steering, where the 1/2 ton always has vacuum assist brakes. The 1/2 ton will have a 4L60E transmission, where the 3/4 ton will have a much heavier-duty 4L80E (or 4L85E if 8.1L, depending on year). They both use the same NV246 transfer case. The rear differential on a 1/2 ton is a 10 bolt 8.5" semi-floating axle, where the 3/4 ton will have a 14 bolt 11.5" full-floating axle. The front differential on the 3/4 ton is 9.25" versus the 1/2 ton's 8.25" gear. The front axles and CVs are larger as well. The wheel bearings and hubs on the 3/4 ton are physically larger, and have side bearings in the rear (full-float) for better lateral-load support.
In my opinion, and in my experience (in half ton GMT800 Subs/Denalis/Escalades too), there is only a 1-3 mpg overall difference between the 'best' 1/2 ton 5.3L 3.73 and the 'worst' 3/4 ton 8.1L 4.10. You're just not going to get better than 17 mpg on the freeway, and no worse than about 14 mpg (my personal experience), and around town not better than 12 and no worse than 9. So 3 mpg delta, at most. Towing you may actually get *better* with the larger motor/gearing as it's not working as hard.
Just my two cents
