I'll answer your first question and leave the rest to others. This is going to read a little like a sermon but please understand that it is not meant that way. It's just an attempt to air out "the rest of the story"
The reason your deuce goes the speed it does is because it was designed that way on purpose. The single circuit brakes of nearly all deuces ,except the M35A3 and similar, is not desigened to stop anything faster. Before you do anything to make the truck go faster you should think about the safety risks to yourself and everyone around you on the road. Even the dual circuit trucks have lousey brakes by modern standards. The only advantage they have is that they will retain some braking ability if a single brake line fails.
One of the principle characteristics of tactical trucks is the relatively high ground clearance and purposely short wheelbase for the overall length and load capacity of the truck. These, along with the height needed for the top loading axles and front drive shaft, allow the vehicle to clear higher obstacles than their civvy counterparts but result in the penalty of having a much higher center of gravity than a civvy truck of similar size and capacity.
The high CG means there is a dramatically increased risk of roll over accidents and higher speed simply aggravate that tendency. Additionally, the higher CG leads to more weight transfer to the outside wheels in a turn or on a curve than is the case with a civvy truck of similar size and weight. The resulting lower load on the wheels to the inside of the curve increases the chance of those brakes locking up when braking. This is especially true of a lightly loaded truck since the brakes are sized for a fully loaded truck. Higher speeds will aggravate that tendency, too, and these trucks are prone to brake locking even when stopping in a straight line at stock speeds.
These trucks were designed to off road operation and unimproved roads with some convoy operations at moderate speeds on improved roads. Before worrying about making the truck go faster the safe and responsible thing to do is to make sure the brake system is at 100% efficiency, change the tires to something with better braking performance and then to make a reasoned decision as to whether the desire to go faster is more important than the very real increased risks to yourself and others.
Time to put the soapbox away....
Lance