... look for diesel/hydraulic hybrids. They are being tested in UPS trucks right now and the results are astounding.
Works well for years in Holder tractors. The diesel-to-pump output pressure can even be electronically regulated and hence pulsed to the drive motors instead of letting them spin freely due to torque. Think of it as ABS-like drive. (not for our use, but additional hydraulic loads can be added (power-take-off) and electronic control priority can be assigned to either the drive wheels or the PTO; with priority assigned to PTO, as the PTO load varies the PTO RPM is maintained - constant velocity PTO!)
Down side is the weight of the hydraulic motors at the wheels - they have to be very robust, as does the pump and the controllers. Fine for a tractor, and apparently a delivery truck, but the pump, hydraulic controllers and motors are a lot of weight compared to a generator and electric motors.
The diesel-hydraulic has to change it's RPM to provide speed control. Electric allows the diesel to run at an optimum RPM/load (optimize efficiency and emissions) and the excess is stored until needed, something hydraulic can't do. I note that Oshkosh is going the route of ultra capacitors, not batteries.