Dan,
First, check the fluid level in the reservoir for the slide pump. If you have hydraulic leveling jacks, you may have two 12V hydraulic systems, so be sure that you check the fluid in the slide operating system.
Next, what is the voltage and amp draw at the hydraulic pump for the slide system when it is operating. If you have low voltage, you have a poor connection that can be at one of the terminals or internally at a relay or circuit breaker. Excessive amperage draw should either trip a breaker or blow a fuse and that would indicate a needed pump motor repair.
Gerald