One thing I hadn't really thought of before, but which was brought to my attention, is that fuel injected setups handle cruise much better without "bogging" like carbs do...you can "lug" the engine a lot more than you can a carb, and still maintain economy.
If you are seriously concerned about MPG, you could keep your eyes open for a more cruise friendly axle set, probably around 3.42. The 465 will easily hide the gear difference probably up to a 33" or so tire (changing to 3.42 from 4.10 with 35's would be more noticeable) so that is a viable option, IF you are that concerned about it.
This is all freeway though. Honestly, I don't think anyone has done anything at one time that netted more than a 2MPG decrease or increase in town. A swap of a big block, 1 ton running gear, and 36" tires would probably ruin in town mileage, but losing the OD tranny alone isn't going to affect mileage in the city noticeably, and more than likely will increase it if you drive sanely.
I ended up with the same in town mileage with my 350/465 combo and my 305/700R4 combo. Dad swapped a BB from 350 into his 3/4 ton with 4.10's, and saw MAYBE a 1MPG decrease in city driving. Freeway was at least 2MPG less, but you can see that weight is a problem in town, and that is almost impossible to decrease enough to notice.
