check the hydro fluid if it is low then there is your problem. I have also run into this problem from clogged filter.
hydraulic system is separate from transmission. there will be a hydraulic level dipstick under the valvechest on the rightside of the truck
I believe on this model the hydraulic oil is checked from the same dipstick in the trans. the pump seal is sure looking like the problem. thanks for the help on this problem.
check that your hyd level is going down. it maybe that your engine is over revving. if the hyd level is going down then the seal in the hyd pump has gone ,it,s bolted into the transmission under the left hand side of the truck. you,ll get a fair bit of oil coming out when you pull the pump so get some trays ready and remember to reset the oil levels when you put new pump in