[Phantom]

If you were to keep the set up I would work on automating the throttle on the electric motor.

Something like this: (e= electric motor throttle, TPS= Throttle position sensor of engine)
If <25mph = 20%e
If TPS >10% = 1-100%e
If Load >x = 1-100%e
If TPS 0-2% and MPH >47 = regen
If brake is applied = regen

The actual percent of applied assist would be based on engine load using the MAP sensor. That way if you can cruse at 70mph with 7-9% throttle normally, but up hills you need 12-25% to maintain 70mph due to the extra load, the controllers throttle will aim to keep the load consistent allowing the car to climb the hill at 12% instead of 25% throttle.