Does the indicator move when you hit the selector button?
I see there is a "speed limiter" wire (white wire) you can connect to limit the speed. This may or may not help.
Good question and suggestion...
I suspect that when you went with the new controller, it's not configured to communicate or operate properly with your old display.
If they are a
matched set, check that the green wire has a good connection from display to controller.
Did you try connecting the two white wires together to limit speed?
As far as the throttle modification, I would recommend the following, with the shown expectations...
This "Double Dipper mod" is shown individually and with more details in this thread under MODIFICATIONS...
Guide to Hall Sensor Throttle operation, testing, and modification.
It would be interesting to see the output voltages of your wayward throttle, when you get things sorted out. But I recommend starting with at least what's happening with the throttle output, before modifying...
Sorry I'm late to the party, but this sounded like a potential different problem.
"the moment i give the throttle a nudge, the motor
jerks a few times then smooths out as a higher speed is reached."
Regards,
T.C.