Controller questions

I have bought off Ebay from a vendor called Yescom, 3-36volt, 800 watt rear wheel hub kits....All kits have been installed on same type of bike, using 22amp batteries

from the same battery supplier....It seems the last kit I have installed is about 25% slower than the first 2 kits I installed.....
The site on Ebay lists several different voltage's & wattage, then you make your choice and pay...The controller that comes with these kits
have a data sticker that has been written on with a marker indicating the volt & wattage....this leads me to believe that the vendor adjusts the
controller before shipment to match the order....does anyone know if this can be true and if so, can I readjust the controller locally....the motor
itself has an 800 watts etching on it...

it's very possible it is adjustable but you'd need some way of measuring the current to the motor at maximum throttle

Look up your controller, I know Kelly controllers are programmable with a USB cable,PC and their free software.