I would check to see if the contactor coil is strong and pulling the contacts in nice and quick. Put a volt meter on the coil and see if the voltage is pulsing on and off. If so, check the the switch in the control handle and your machine may a a lift limit switch the shuts off the high speed (M) contactor when the forks are raised over 24". If the wiring and switches all seem ok then it may need a new auxiliary card.