BB forks, try this remove the return hose of the control valve ,attach another hose and drop it in a bucket, put your mast up and then drop it if the oil stops more or less quickly then you have a hoist cyl problem, if it runs on a few seconds this may be an indication the problem is in the valve, this valve isn't controlled by solenoids is it, I know I experienced a similar problem on a Yale truck with a triplex mast and it turned out to be a check valve in the control valve slow to seat.

Titus