I'm dealing with a problem on a counterbalance truck that I think is likely related to the thing you're experiencing at least in terms of how the logic board solves the problem of limiting travel speed.

It limits voltage by.375 (1/3) a volt per value of speed limit from 0-255 steps. even when your wheel is straight, I assume there is some speed limit in effect, and so something about the way this calculation is being processed is over estimating the need for speed limiting. In my case, it's limiting me to 3.5 volts power to the t2, which is insufficient to activate the traction motor contactors I haven't isolated the cause of the speed limit, and I don't have an LX handset so I'm rather stumped atm, but I'm definitely considering buying one because I hate not being able to solve a problem.

Would you have access to a code reader somehow? Someone on the forum might be able to look up the code for you if you can get it to read out somehow. I think there's also a memory slot that stores the last code even if the code isn't currently active, because the machines been rebooted/power cycled, but I don't know where that value is stored or how to access it.

FSIP has some pretty informative manuals on the GE controller EV100 in my case, though it's a newer machine so i'm not sure if you've got the 100 or I don't know if it was the 10 or the 1000 before that. I'm pretty new to this.