And those high voltages give you an ultimate efficiency as well
All you need to figure out, is ho your going to drop in those cells.
20 GP3300's can push your truck faster than you want to. (100km/h, i can't imagine that's your goal)
You could consider 18/20 cells on a 2240/8. (with a 36120 controller)
check
this link to see the torquemonster on 21V in action.
It has got twice the torque of the bigmaxximum, that will push a heavy truck around quick.