The difference in mpg for these two gears is almost negligible... maybe 1mpg at most. The reduced low-rpm efficiency of a larger cam will cost more than that.
The metric size you list corresponds to a 32.2" tire height. Is the 15.3 1/4 mile time you list with the current mods? What was the trap speed? For simplicity's sake I'll assume 100mph for the remainder of the discussion.
You have two directions to go here... you want better highway efficiency/manners or do you want better dragstrip performance?
Using a gear calculator, your current setup (32.2" tires with 3.42s) cruises at 75mph turning about 1900rpm, correct? With 3.73s you will cruise at 75mph turning about 2050rpm (which is the same as a 2004 yukon with 3.73s and 31.5" tires... the ones on the 17" factory wheels, including Denalis). With 4.10s you will cruise at 75 turning ~2250rpm. A little more noise will be present, but depending on your exhaust you many or may not get drone at these rpm. Drone will drive you crazy on long drives since the distorted wavelengths will act like a constant base sub vibrating in the cab at an annoying rate.
At the dragstrip, 3rd gear with 3.73s at 100mph is turning about 4k rpm. With 4.10s 100 is at 4300rpm. For best performance you want to cross the line at 2-300rpm past your hp peak rpm in the direct gear which is 3rd in a 4L60E (I call this out due to the limited gears and wide gear spacing like the 60E has). If your cam and mods peaks on the dyno at 5800rpm (typical of a 220/220 cam with non-ported heads), you want to be crossing the finish line turning about 6000rpm at the top of 3rd gear... which to do that you will need to drop the tire height down to about 30" and run a 5.13 gear, or a 28" tire with 4.56s... both give approx the same running ratio. In the case you have two sets of tires and the ability to program the PCM on the fly for the new size to get the shift rpm/mph correct (the 28"/4.56 track setup for reference), then on the highway your 32.2" tires with 4.56s will turn 2500rpm at 75mph. You might not like this many rpm on the highway as it will be louder.
As a side note, if you did change to 28" tires and 4.56s for dragstrip use, your 1/4 mile time would drop 5 tenths, easy.
As you see there will have to be some major compromise on the two different goals at hand.
This probably isn't an option, but I'll throw it out for you to consider.
The only real way around this is to swap in a 6L80E and run 3.73s or 4.10s. The 6L80E has a much wider and deeper gear range that will give you loads of launch torque with narrow shift extensions during the run. For example, a 4L60E's first gear is a 3.06:1 ratio and with 4.56s you have a 13.95:1 launch ratio. A 6L80E has a 4.03 1st gear and with 3.42s has a 13.78 launch ratio. Correspondingly, the 6L80E with 3.42s in 2nd and 3rd gear closely resembles a 4L60E's 2nd and 3rd gears with 4.56s (simple math to get total reduction). You will cross the line in 3rd gear, but again, the 6L80E has much deeper gearing to compensate for the taller tires and gears. The gear calculator shows 32.2" tires with 3.73s and the 6L's 0.67 6th gear ratio will cruise 75mph at around 1980rpm, close to what you currently turn with the 4L60 and 3.42s with your tires. It will take a heap of work to do this swap in an 01 though.
