By going into high speed, do you mean that the by-pass contactor is closing, or that it's running at full SCR speed?

It's been a while since I've worked on an EV1 30sc, but I'm pretty sure that it will have two switches in the accelerator control box. One for start and the second for full speed by-pass contactor command. Check that the by-pass command switch is working, also check the accelerator potentiometer is working. These checks should be made at the input terminals at the EV card.

You did say this is a 30sc, but said you had "the" drive motor rebuilt, SCs are dual drive motor machines, I want make sure we are on the same page.