I'm loosely part of the Irish driving instructor community as i have been training to be one, and while i'm not a mechanic i do know a good bit about how vehicles feel and drive and operate. Driving instructors would agree that second gear is a superpower, even the smallest engines can make a steep hill trivial in 2nd. I'm guessing a 2.5 tonne truck could easily spin it's wheels in 2nd with a full load. 1st is slow but massively strong, its used for only 2 things, taking off, and moving the earth under the wheels with little resistance. But second is the one that you rely on for turning corners, roundabouts, and it has excellent balance between speed and maneuverability. I'm guessing 2nd, is what you would use to get over a significant obstacle in reality. See if i have to make a square turn efficiently?, i have to slow down to where a speed in 2nd is comfortable...not because i'm trying to do a racing turn around the bend at speed, but because its not reasonable for me to expect i can turn the wheel fully for a square turn in the time expected.
if im to get around a turn with reasonable efficiency, my wheels need to be "engaged" with the ground, meaning i'm giving it a little gas, but also i have to be able to expect air-brake a little also. But there is also the issue of the reduction in power dropping a gear from 3rd to 2nd and that helps with the air-braking, and of course, you give it a little brake peddle too before going into a turn.
I think the gears in squad should be manual. and as you descend through the gears, i think there should be an air-brake mechanic and each gear should have a suitable "moving the earth below the wheels" value, that is not the same as the torque btw, and i expect it's not an easy thing to get right what with all the terrain types (mud, grass, asphalt etc).
That being said, the M35A2 Deuce has to hawl a lot of ass to get over some of squad's terrain obstacles, and drivers in the game should manage their expectations. Check out this small video, and bare in mind, that wet mud is the WORST case scenario.