ASV 4800 Sluggish hydraulics after unit is warmed up

I have a 1998 ASV 4800. When the unit is warmed up the hydraulics get real sluggish it seems like the motor gets bogged down almost like he can't push the hydraulic fluid I can't dig and move at the same time it'll stall the motor any suggestions on what to look at I've checked the filters they're fine and I am using the correct hydraulic fluid