I vote for gears...4:10s on a truck with 285/33 inch tires will bump the power band back into the the torque/hp curve of say 235/245 tires and your 3:55s. With 35 inch tires, 4:56 gears is the recommended, but I understand 4:88s are availible.
Now a lighter vehicle like a short bed regular cab might get away with 4:10s and 35's
Lets not forget that larger tires weigh more and therefore take more torque to get moving. They are torque eaters...and although a high stall converter would help there is a downall...they generate more heat. In a transmission known for its abilty to meltdown without warning, this is a bad thing.
Gears, on the other hand, provide instant response and torque multiplication. Imagine almost 80 or more ft lbs of torque instantly applied to your tires the moment you touch the gas. As far as mileage goes, there is a "potential" at certain speeds to increase your mileage because your motor isn't lugging down, and your tannny will probably not hunt as nmuch for OD on hills
There are two disadvantages to gears...the first, cost. It's not cheap to regear. However I can assure you after some 30 plus years of modifying and racing motor vehicles that no mod gives your ride more "attitude" than gears.
You can add more motor mods like headers, rockers, and the like, but untll you radically change the off idle torque output, you will not achieve the results you seek.
The second is that while gears are torque increasers, they are horsepower eaters. So your top end will go down. You will not be able to go 100+ mph anymore with your truck. You could probably build up a motor with those other mods to do so, but I would have to question your sanity.
EDIT: here's a handy gear/rpm/tire chart to help you. Don't forget to subtract at least 15% off your rpm for OD or 5th gear!