If you want to run any kind of safe speed think 55,000 watts at a minimum since the electric motor doesn't develop a lot of Horse Power at low rpms you may need even more power. The generator is not going to operate any more efficiently than a bigger motor in the vehicle already. You are trying to move too much vehicle and that can't be done efficiently unless you make it more efficient at converting gasoline to mechanical energy. Even with a small bank of powerful output Batteries and the generator you still are limited to the gas motor in the generator and the size of the vehicle.
It is possible. Diesel Electric locomotives have successfully used this technology for decades. The rational is that tremendous loads can be moved from a dead stop. The drive wheels are relatively small compared to vintage steam locomotives so no transmission is actually needed. True we are talking about LOAD MOVING and electric motors put out high torque at low speeds. For the pickup truck, you do need probably 2000 pounds of batteries (48 batteries for starting draw of 80 amps each for 48 hp) Then the generator could charge the batteries plus regen braking could also help charge batteries. Without the generator, you could run the truck for about 120 minutes @ 25 amp draw for each battery which would be approx 12 hp total just to drive down a level road. Probably get you 60 miles tops. So, back to the gas electric model just think about the Prius hybrid or locomotives and try an engineer your vehicle around that concept. I'll concede that losses are significant but put your thinking caps on.
It is possible. Diesel Electric locomotives have successfully used this technology for decades. The rational is that tremendous loads can be moved from a dead stop. The drive wheels are relatively small compared to vintage steam locomotives so no transmission is actually needed.
I think you have this mixed up. I don't think the size of the drive wheels has anything to do with not needing a transmission. Whether you have big wheels that need a transmission for lower gears or small wheels that need a transmission for going faster, you'd still need one. The reason diesel locomotives don't need a transmission is just because it uses electric motors. The big advantages to not having a transmission are weight saving, fewer moving parts, and less maintenance on not only the transmission, but the diesel motor itself. A motor that needs to only operate at a certain RPM for sustained periods lasts much longer than one that constantly changes RPMs (think highway miles vs. in-town miles in a car and their effect on the longevity and wear on the motor). Other advantages include electric motors just being more efficient than a transmission, having each axle powered by its own electric motor (instead of having them all bolted together like steam engines), and each electric motored axle is independently controlled, meaning that if one slips power can be adjusted. Wheel slip is one of the biggest problems a locomotive can have.
You can't have a direct mechanical connection from the engine to the wheels in a train because that would require unbelievable torque and an clutch to handle it when trying to get the train moving from a stop. The electric drive takes care of this.
You could even put a generator and drive motor on a bicycle and if setup properly it would allow you to crank your brains out at any speed and get really great acceleration off the line and any top speed you want without having to pedal faster as you went faster. Sort of an infinately variable transmission.