I don't think the capacitor is giving you problem. Anyway you can test its capacitance with a multimeter. Remember to discharge the capacitor. If this unit was having fast speed before, then adjustment of speed is not necessary, unless somebody had done that. You need a service terminal to adjust parameters.
It seems that your unit is sensing that it is always outside the aisle, turret head and forks are not in home position. That is why you get only slow speed. However, check all the switches wires at their termination point to make sure that they are really connected. Sometimes the switches are good, but you have broken wires along the way. Also check the steering. Also check on the mast switches, you could have problems with the mast cables. Quite common to have problem with the 8 core mast cables.
Easy way to check on guide wheel switches is to jack the back up and steer the drive wheels out of straight position. Then push in the guide wheels, you need another person to help so that the 2 switches are closed. The wheels will automatically move to straight position.
I have not worked on Crown trucks for quite some time. I am semi-retired.