I love the troops riding on the back, very nice touch.....is that part of the vehicle, like the BTR-70's or is it done with setpos? Definatly something that has been needed, as it makes the tank so much more useful.
Oh and is the M4A3 only coming in 76mm or 75mm (not sure if the M4A3 had a specific gun) and if so, are you going to make different types, like a 76mm, a 75mm, and a 105mm (short barrel)?
Oh and couldn't tell from the screen shot, but are you going to have a .50 cal on top of the turret?
Great job though!