EZip Trailz
There is a limit for reduced gearing ... about 11%, using a 22T motor side freewheel.
Overvolting (36V?) would give you more torque, but mainly, more speed.
With 36V you could have 50% more torque at 12mph and faster.
But heat production is also increased.
If the hill climbs were short and occasional, higher voltage might be your best bet.
Alternately, expensively and ideally you would run the motor through the 7 speed rear cluster for 2x -3x the torque in low gear.
Still hunting for the affordable method!
In the mean time ..
gain speed before starting hills and pedal hard to maintain,
Remember that eZips are primarily designed as electric assist (eaBikes) not as electric motorcycles (eBikes).